Cesc Fabregas will play no part in Arsenal's Champions League clash with Porto on Tuesday night.
The Gunners are looking to turn around a 2-1 deficit in the last 16 second leg at the Emirates, but they will have to do so without their talismanic captain.
Fabregas aggravated a hamstring problem in his right leg during the 3-1 win against Burnley on Saturday and he was unable to train with his team-mates on Monday morning.
And manager Arsene Wenger has now confirmed he will not risk the Spain international.
'We cannot even take a gamble, so he is not available,' said the Frenchman.
'I was hoping he would recover after the Burnley game because we were cautious with him.
'We don't know how long he will be out. He is having a scan today and we are convinced it will only be a small time, and he has a small chance of getting back for next weekend against Hull, but to play him again would mean significant damage.
'Ideally we wanted him to be there, but we want to qualify and theabsence of Cesc is no excuse at all. We have enough players and astrong enough squad to get round that and haveenough chances to qualify.'
AVAILABLE FOR ARSENALAlmunia, Fabianski; Sagna, Clichy, Vermaelen, Campbell, Silvestre; Eboue, Traore, Eastmond, Denilson,Nasri, Diaby,Song; Walcott, Arshavin, Bendtner, Eduardo, Vela.
Fabregas limped off after scoring the opening goal against Burnley. Thetightness was in the same hamstring he injured earlier in the season,which kept him out of action at the turn of the year.
Veteran defender Sol Campbell did, however, join in training and he looks set to recover from a groin problem in time to face the Portuguese champions.
Alex Song missed the Burnley match because of a domestic suspension, but he is available to play in Europe.
Andrey Arshavin and Abou Diaby could both feature after coming offthe bench in the weekend Barclays Premier League tie, while Mexicostriker Carlos Vela could return to the squad after international duty.
WilliamGallas (calf) is still sidelined, while Aaron Ramsey (broken leg),Robin van Persie (ankle) and Johan Djourou (knee) are long-termabsentees.
He shoot, he scores.Cesc Fabregas nets as many as he sets up
With Fabregas out, France international Samir Nasri could move into the centre of midfield, alongside Cameroon defensive midfielder Alex Song, whose domestic two-match ban does not apply in Europe.
Wenger feels 22-year-old Nasri - who suffered a fractured leg in pre-season - has come a long way since arriving from Marseille during the summer of 2008.
'In the last few weeks he has got stronger and more confident,' said the Arsenal boss. 'He is very versatile, can play defensive midfield, attacking midfield and on the flanks. We have a few players like that and I love that.
'Samir has adapted very quickly. He is a very intelligent boy, aquiet boy, he analyses what is happening on the pitch very quickly andhas good technical potential.'
Arsenal have not overturned a first-leg deficit in Europeancompetition since the UEFA Cup tie against Hajduk Split during the1977-78 season.
Instructions: Wenger (far left) talks to his squad in training on Monday
In the Champions League, the Gunners went out after an away defeat to Bayern Munich in 2004-05, lost to PSV Eindhoven in 2006-07 and exited the competition last season to Manchester United after being outplayed over both legs.
Wenger, though, maintains tomorrow will be different.
'This time, we have scored,' said the Arsenal boss. 'When you lose 1-0 away from home it is a difficult game because when you start the next game you know it is almost over because you have to score two or three goals to qualify.
'This time it is different - if we score one and do not concede then we will qualify.'
Porto were thrashed 4-0 on their last visit to Emirates Stadium during September 2008 - the Dragon's worst away reverse in the competition.
Wenger feels that result will count for nothing when the Portuguese side return to north London tomorrow.
He said: 'I do not think anyone will be complacent. We know it will be a tricky game, but we believe we can do it. We have good confidence, we are in a good position, so let's go for it.'
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