Tomas Rosicky is also anticipated to be fit following a groin problem, but Gallas has "an endless calf injury", according to Arsene Wenger.
Gallas has missed the last six games and is set to be out for at least two more matches - missing the Hammers contest and the match at Birmingham on March 27.
"Cesc and Tomas have a final test on Friday morning," Wenger told Arsenal TV Online.
"They should be available for Saturday.
"From the last game we don't lose anybody. So normally we should have Fabregas, Carlos Vela and Rosicky back. Plus of course we have Song coming back from suspension.
"However, William Gallas will not be available this week or at Birmingham. It is going on and on. It is a concern.
"It is an endless calf strain and so we need Sol Campbell and Mikael Silvestre to be highly ready to help us out."
Alex Song will be back from a two-match suspension against the Hammers and Carlos Vela could be added to the squad as Arsenal seek to enhance their title bid after their last-gasp 2-1 win at Hull last weekend.
Arsenal 2/9, Draw 9/2, West Ham 14/1