The 32-year-old limped out of Arsenal's Champions League quarter-final first leg against Barcelona after suffering a recurrence of his calf injury.
Gunners boss Arsene Wenger admitted his gamble on the veteran defender - who had not played for six weeks - failed to come off, as he was ruled out for the rest of the season.
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France manager Raymond Domenech was less than impressed by the whole situation, but Gallas believes he will be fit to join up with his country ahead of the trip to South Africa.
'I wanted to play this game against Barcelona, because I am a competitor,' Gallas told French TV station CanalPlus.
'I want to play against the best players and I had an agreement from the medical staff and fitness coach.
'Now my objective is not to suffer any relapse and I am confident. If you are not confident, you can forget about the World Cup.'
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