Fabregas was already ruled out of the Champions League quarter-final second leg after picking up yellow card in his side's 2-2 draw in the Emirates Stadium.
But the 22-year-old then suffered a suspected broken leg and could be sidelined for the rest of the season.
Leave it to me Cesc: Nasri gives Fabregas a pat on the back after the Arsenal captain, in obvious pain, scored from the penalty spot against Barcelona
Nasri deputised for the injured Fabregas in the previous round against Porto and scored a superb goal in the 5-0 home win. And Denilson is hoping for more of the same.
He said: 'We are sad now because Cesc is a brilliant player/ But I think Samir can come in to help us, and it is more important to go there and to win.'
Zlatan Ibrahimovic's brace gave Barca a deserved 2-0 lead in north London before Theo Walcott and a Fabregas penalty hauled the Gunners level.
Confident: Denilson believes Arsenal can get a result in Barcelona on Tuesday
Goalkeeper Manuel Almunia kept his side in the game with a string of saves early on before the hosts pulled off their remarkable comeback.
Denilson added: 'In the first half they played better than us. But you just continue to focus in this situation and we have one more game to go through.
'It was a great opportunity to show (the team's spirit). We started very, very badly, but in the second half we played more, passed the ball. But I think we played well in the second half.'
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