Cesc Fabregas has been ruled out of Arsenal's Champions League last 16 second leg game against FC Porto at the Emirates Stadium on Tuesday.
The loss of his captain is a devastating blow to Gunners boss Arsene Wenger as his side look to overturn the 2-1 lead that the Portuguese side picked up in controversial circumstances three weeks ago.
Fabregas came off not long after scoring in the 3-1 win over Burnley at the weekend and the hamstring problem that forced that substitution means he will miss the Porto decider.
In better news for Wenger, veteran centre-back Sol Campbell has recovered from a groin problem and should displace Mikael Silvestre in central defence with William Gallas still sidelined with a calf injury.
Alex Song could come into the midfield after being suspended for the Burnley game, while Andrey Arshavin and Abou Diaby could also both feature after coming off the bench against the Clarets and Mexico striker Carlos Vela may be back in the squad after international duty.
Aaron Ramsey, Robin van Persie and Johan Djourou are long-term absentees.
Midfielder Raul Meireles and centre-back Rolando were rested by Porto at the weekend but can be expected to play for Jesualdo Ferreira's side in London. Highly-rated strike duo Hulk and Radamel Falcao should lead the attack as the 2004 winners look for a first ever competitive win on English soil at the 14th attempt.
Arsenal (from): Almunia, Clichy, Vermaelen, Campbell, Eboue, Denilson, Nasri, Song, Walcott, Arshavin, Bendtner, Fabianski, Sagna, Diaby, Eduardo, Traore, Eastmond, Silvestre, Vela.