The Arsenal player, France's best remaining specialist centre-back, sat out yesterday's session and was being assessed before training today ahead of Thursday's clash with Mexico.
Gallas was partnered at the back by Barcelona's Eric Abidal, a left-back by nature who can play centrally, in the disappointing 0-0 draw with Uruguay in Cape Town on Friday.
Wait and see: France defender William Gallas (left) vies for the ball with Djibril Cisse
Gallas - who was reportedly angered to be overlooked for the captaincy which went to Patrice Evra - is thought to have only experienced slight muscle discomfort and was rested in training as a precaution.
France coach Raymond Domenech is reportedly set to restore Florent Malouda to his starting line-up having left him on the bench against Uruguay.
Zidane claims France are not a team and Domenech is 'not a coach'Ian Ladyman's World Cup diary: Blow the other one Evra, you were just bad Uruguay 0 France 0: Domenech's men flop in opener after Malouda bust-up FRANCE WORLD CUP PAGE