The defender has been out for five weeks with the injury, which he fears could be connected to a niggling back problem.
No end in sight: William Gallas has been out for five weeks
Wenger said: '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 help us out.'
Fabregas should be fit after a hamstring injury to face West Ham tomorrow and Alex Song will return after suspension.
Gallas's fitness problems have coincided with contract talks about extending his stay at the club, but the Arsenal manager has insisted Gallas, 32, must accept reduced terms on any new deal.
Wenger is ready to offer Gallas a deal until 2012 but only if the player cuts £30,000 off his £80,000-a-week deal, with the www.dailymail.co.uk/sport shortfall made up by bonuses.