London (AFP) - Juan Martin del Potro was forced to withdraw from Queen's Club with a knee injury despite winning his first round match on Wednesday.
The Argentine injured his right knee towards the end of his 7-5, 6-4 win over Denis Shapovalov after slipping on a damp court.
The 2009 US Open champion was playing in only his fifth tournament of the season after fracturing his right kneecap last October.
Del Potro was due to face Feliciano Lopez in round two, but the Spaniard will now have a bye into the quarter-finals.
Lopez also had an eventful day too as he was forced to strenuously deny reports in Spain that a match he and doubles partner Marc Lopez lost at Wimbledon in 2017 was fixed.
"I feel it is extremely important to come to you and absolutely deny any link with the events described in relation to the allegations of match fixing," said Lopez after coming from a set down to beat Marton Fucsovics 6-7 (4/7), 6-3, 6-4.
Lopez is due to partner Andy Murray on his return to court after hip surgery in the doubles.
Three-time Grand Slam champion Stan Wawrinka overcame a series of rain delays to beat Britain's Dan Evans 6-3, 6-4.
However, three first round matches are still to be completed after rain washed out much of a second consecutive day's play.
Top seed Stefanos Tsitsipas took the first set against Kyle Edmund before play was finally postponed.