Rafael Nadal of Spain plays against Nikolay Davydenko of Russia in a Singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25, 2009. TOPSHOTS AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Rafael Nadal of Spain is pictured after losing to Nikolay Davydenko of Russia 6-1 7-6 (7-4) in their singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25. After the loss, Nadal said he was going work hard on regaining his self-belief and sharpness in a bid to reclaim the world number one spot from Roger Federer next year.

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain serves during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Julian Finney/Getty Images)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain serves during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Julian Finney/Getty Images)

Spain's Rafael Nadal serves the ball to Russia's Nikolay Davydenko during their ATP World Tour Finals tennis match at the O2 Arena in London, Wednesday Nov. 25, 2009.

Spain's Rafael Nadal reacts during his ATP World Tour Finals tennis match against Russia's Nikolay Davydenko at the O2 Arena in London, Wednesday Nov. 25, 2009.

Rafael Nadal of Spain plays against Nikolay Davydenko of Russia in a Singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Spain's Rafael Nadal changes his shirt during his ATP World Tour Finals tennis match against Russia's Nikolay Davydenko at the O2 Arena in London, Wednesday Nov. 25, 2009.

Rafael Nadal of Spain plays against Nikolay Davydenko of Russia in a Singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Spain's Rafael Nadal, right, reacts to point against Russia's Nikolay Davydenko during their ATP World Tour Finals tennis match at the 02 Arena in London, Wednesday, Nov. 25, 2009.

Spain's Rafael Nadal reacts to point against Russia's Nikolay Davydenko during their ATP World Tour Finals tennis match at the 02 Arena in London, Wednesday, Nov. 25, 2009.

Rafael Nadal of Spain is pictured after losing to Nikolay Davydenko of Russia 6-1 7-6 (7-4) in a Singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25, 2009. AFP PHOTO/GLYN KIRK (Photo credit should read GLYN KIRK/AFP/Getty Images)

Spain's Rafael Nadal changes his shirt during his ATP World Tour Finals tennis match against Russia's Nikolay Davydenko at the O2 Arena in London, Wednesday Nov. 25, 2009.

Spain's Rafael Nadal returns the ball to Russia's Nikolay Davydenko during their ATP World Tour Finals tennis match at the 02 Arena in London, Wednesday, Nov. 25, 2009.

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain reacts during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Matthew Lewis/Getty Images for Barclays ATP Finals)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain reacts during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Matthew Lewis/Getty Images for Barclays ATP Finals)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain reacts during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Matthew Lewis/Getty Images for Barclays ATP Finals)

Rafael Nadal of Spain (R) congratulates Nikolay Davydenko of Russia after losing 6-1 7-6 (7-4) in a Singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25, 2009. AFP PHOTO/GLYN KIRK (Photo credit should read GLYN KIRK/AFP/Getty Images)

Rafael Nadal of Spain (R) congratulates Nikolay Davydenko of Russia after losing 6-1 7-6 (7-4) in a Singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25, 2009. AFP PHOTO/GLYN KIRK (Photo credit should read GLYN KIRK/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain reacts during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Matthew Lewis/Getty Images for Barclays ATP Finals)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain returns the ball during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Matthew Lewis/Getty Images for Barclays ATP Finals)

Spain's Rafael Nadal reacts to point lost to Russia's Nikolay Davydenko during their ATP World Tour Finals tennis match at the 02 Arena in London, Wednesday, Nov. 25, 2009.

Spain's Rafael Nadal returns the ball to Russia's Nikolay Davydenko during their ATP World Tour Finals tennis match at the O2 Arena in London, Wednesday Nov. 25, 2009.

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain returns the ball during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Matthew Lewis/Getty Images for Barclays ATP Finals)

Spain's Rafael Nadal reacts during his ATP World Tour Finals tennis match against Russia's Nikolay Davydenko at the O2 Arena in London, Wednesday Nov. 25, 2009.

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain reacts during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Matthew Lewis/Getty Images for Barclays ATP Finals)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain returns the ball during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Julian Finney/Getty Images)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain serves during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Clive Brunskill/Getty Images)

Rafael Nadal of Spain gestures as he plays against Nikolay Davydenko of Russia in a Singles match during the Barclays ATP World Tour Tennis Finals in London, on November 25, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 25: Rafael Nadal of Spain returns the ball during the men's singles first round match against Nikolay Davydenko of Russia during the Barclays ATP World Tour Finals at the O2 Arena on November 25, 2009 in London, England. (Photo by Clive Brunskill/Getty Images)