The tightness was in the same hamstring he injured earlier in the season, which kept him out of action at the turn of the year.
Related ArticlesArsenal set for Fabregas gambleAlan Hansen: Walcott must learn fastFabregas: I've been lucky to escape bad injuryInjury worry for Rooney and FabregasWenger: fear of injury holding Walcott backArsenal 3 Burnley 1The decision for Fabregas to sit out training may be precautionary with Arsène Wenger suggesting he will gamble on the playmaker's fitness for tomorrow night's match at the Emirates.
'He has a little chance to be fit,' Wenger said following their win over Burnley. 'I'm ready to take the gamble but, if it is more than a 50 per cent chance that his hamstring goes, I will not take it.'
Veteran defender Sol Campbell did join in training and he looks set to recover from a groin problem in time to face the Portuguese side, who will take a 2-1 lead to north London.