Uncertainly about the fitness of Gallas, who is recovering from a calf injury, is the reason why France coach Raymond Domenech named a provisional squad of 24 players instead of the official 23.
Over the past few days, France's most reliable and experienced defender has been training at the team camp in the French Alps resort of Tignes, raising hopes he would be fit to play in the June 11-July 11 finals.
"William is our main man at the back and we need him," Clichy, who plays alongside Gallas at Arsenal, told reporters on Sunday.
"I have no doubt he will play at the World Cup," Clichy added. "He has hiked up with us in the snow and has been training with no problems. I know him well, he's strong, he won't give up and he will make the trip with us."
Squillaci, too, was confident Gallas, who suffered a recurrence of left calf muscle injury late in March and has not played since, would board the plane to South Africa.
"From what I see, he's physically fit and he will stay with us until the end," Squillaci said.
CAUTIOUS DOMENECH
Domenech, however, is extremely cautious since he took an injured Patrick Vieira, then the France captain, to Euro 2008.
The decision proved controversial as Vieira was unable to play at all in a campaign that ended with a shock first-round exit.
"There is room for optimism but it's still a calf injury and we don't know what can happen," Domenech told French television channel TF1 on Sunday about the Gallas situation.
Former Arsenal skipper Gallas could face his first real test on Wednesday when he is expected to be picked for a friendly against Costa Rica, the first of three warm-up games for France.
If Gallas were declared fit, Domenech, who has 23 players left at his disposal after midfielder Lassana Diarra was ruled out by illness on Saturday, would have two options.
He could stick with the 23 still in Tignes or take a player out and bring in a replacement for Diarra before the June 1 deadline for teams to announce their official 23-man squads.
"We won't hurry, we'll take our time before finding a solution, providing we need to find one," Domenech said.
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