XArsenal central defender William Gallas will be out for "a few weeks" after suffering a thigh injury in training on Monday (November 20), coach Arsene Wenger said. Wenger, whose side were preparing for Tuesday's (November 21) Group G Champions League game at home to Hamburg SV, said the Frenchman suffered the injury at the very end of the session at their London Colney base. "We've lost Gallas in the final shot of training," Wenger told a news conference. "He pulled his thigh and will be out for a few weeks." Losing Gallas, who joined from Chelsea on transfer deadline day in August in a swap with Ashley Cole, is a major setback for Wenger both in Europe and domestically. Swiss internationals Johan Djourou and Philippe Senderos would be the main candidates to replace him on Tuesday, when Arsenal need to get their campaign back on track. Arsenal, who beat Hamburg 2-1 away in a promising start in Group G, have taken only a point from their last two games against CSKA Moscow and are level on seven points with Porto. With the Russians top on eight points and Hamburg out of the running after four straight defeats, Arsenal's campaign will go down to their final match at Porto on Dec. 6. Wenger said two players who missed Saturday's 1-1 draw at home to Newcastle United -- Brazilian midfielder Gilberto, who returned home for family reasons, and Fredrik Ljungberg, who lacked match fitness after injury, were ready for duty. Dutch forward Robin Van Persie, who limped out of Saturday's game but trained on Monday, is also fit. Wenger is hoping that his team will improve on Saturday's performance against Newcastle. "We have to play relaxed and focused," he said. "After I feel, the rest come usually along. We have not to put too much pressure on ourselves, but of course we have to be more dynamic than against what we produced against Newcastle in the first half because that was not our usual way and not how we want to play football." Wenger has thrown his weight behind calls for referees to use video technology. The issue is back on the agenda after Blackburn Rovers manager Mark Hughes and Watford's Adrian Boothroyd called for technology to be used in the wake of controversies last weekend. Asked if he backed the use of replays by referees, Wenger told a news conference on Monday: "I feel it's difficult to defend, to refuse progress. You want the right decision to be taken, and every week now, every game is detailed, every decision of the referee is on television and analysed and the only on the whole game who has no access to video, the right image, the right picture, is the referee. I don't find it right, but what is even more surprising is that the referees don't want to use it." Wenger's comments echoed those made by Hughes, whose team had a penalty appeal turned down in their stormy Premier League draw with Tottenham Hotspur on Sunday. "I've never been an advocate of technology but sooner rather than later they should bring it in," Hughes had said. "When huge decisions at the top level have an impact on teams, management and players then something has to be done." Boothroyd gave his backing to technology for referees after his side's defeat by Portsmouth on Saturday.