Arsenal's chances of beating defending champion Barcelona in the first leg of the Champions League quarterfinals Wednesday could be severely dented before kickoff at Emirates Stadium. Cesc Fabregas is Arsenal's leading scorer this season with a remarkable 18 goals in 35 matches from central midfield but he is receiving treatment to a knee injury and sat out training Tuesday. With coach Arsene Wenger having tweaked his formation to give the 22-year-old Spain international greater freedom in attack, his absence would leave a big hole against the club with the second-tightest defense in the competition. Wenger has acknowledged the futility of trying to muscle and mark Barcelona out of the game, so Fabregas is arguably the key figure in the Gunners' efforts to outpass or outscore the Spanish team. “He has gained more physical power,” Wenger said. “You can see he resists much more the runs of his opponents and he is more powerful in his runs. These two ingredients make a big difference.” Wenger is confident the 22-year-old Fabregas will recover sufficiently following intensive treatment on the damage he did in Saturday's 1-1 English Premier League draw with Birmingham. Fabregas' ability to drift unmarked into attacking positions or carry the ball there himself would be missed, but maybe not as much as his composure in possession and accurate passing. That's because the key to Barcelona's defensive success is the fact that other teams simply cannot get hold of the ball.