By Iain Rogers
BRASILIA, July 4 (Reuters) - When guitarist George Harrison briefly walked out on The Beatles in early 1969, John Lennon reportedly threatened to replace him with Eric Clapton.
Sadly for Argentina, coach Alejandro Sabella does not have the luxury of inviting a talented outsider into his "Fab Four" to replace misfiring striker Gonzalo Higuain for Saturday's World Cup quarter-final against Belgium.
Higuain, along with Lionel Messi, Sergio Aguero and Angel Di Maria, is part of one of the most fearsome attacking quartets in international football but has yet to find the net in four games at the finals in Brazil.
His disappointing form marks a sharp contrast with the last edition of soccer's global showpiece in South Africa, when he scored four times in Argentina's run to the last eight.
He also finished as the nation's second top scorer in qualifying for Brazil with nine goals and has 20 overall in 40 appearances for the South American nation.
There is no question the France-born 26-year-old has the talent to succeed at the highest level but he has appeared frustrated and out of sorts.
He did come into the tournament after picking up a leg injury playing for his club Napoli at the end of April but he has featured in all four of Argentina's games without making much impact.
He had a decent first year in Serie A after leaving Real Madrid, scoring 17 goals in 31 games in all competitions as Napoli secured third place and a place in the playoffs for next season's Champions League.
Sabella noted at a news conference on Friday that Higuain had run more than any other Argentina player in the 1-0 last-16 victory over Switzerland.
The player's contribution to the team with his work rate and his tracking back was also important, the coach said, adding that Higuain was "improving every day".
"He was in a lot of pain (after his injury) and was unable to train at 100 percent," Sabella told reporters at the national stadium in Brasilia.
"He sacrificed himself for the team (against Switzerland) and was trying to occupy the spaces.
"We all have a lot of confidence in him because he is a great player.
"He is doing great work for the team but missing a goal. He has had chances but just hasn't been able to convert them."
Higuain is likely to lead the line again against Belgium on Saturday, when Aguero could make his return from injury after missing the Switzerland clash.
The winners will play the Netherlands or Costa Rica in the last four. (Editing by Ed Osmond)