Arsene Wenger hopes Cesc Fabregas' hamstring injury will only keep him out for two weeks - but says Emmanuel Eboue faces up to eight weeks out.
Gunners captain Fabregas was set to undergo a scan on Thursday afternoon to determine precisely how long he would be sidelined for but manager Wenger was optimistic it would be a short hiatus.
"Fabregas will be assessed today with a scan," Wenger told Arsenal TV Online before training on Thursday.
"After that, we can tell you how long he will be out, but I count two weeks."
However, Wenger hinted Fabregas - who has had real problems with the hamstring in his other leg this season - might need to have his game time rationed when he returns.
The Gunners boss added: "It is a big blow because it will question how cautious we have to be in the future with him.
"Cesc has played 50 games a year since a young age.
"We may have to be more cautious with him, especially in the next two months."
Fellow midfielder Eboue, who was carried off on a stretcher in Portugal on Tuesday night, faces between four and eight weeks out with a knee ligament strain.
Wenger said: "It can be four weeks, can be six weeks or can be eight weeks. But I think it will be four weeks minimum.
There were no other injuries from Tuesday, while Aaron Ramsey and Manuel Almunia are progressing along the comeback trail.
Wenger said: "We have a lot of bumps and bruises but everyone else should be available.
"Almunia should be capable to play but I will see how he reacts.
"Ramsey needs competitive games. He played 45 minutes (in the reserves) and he did well.
"We need to get him slowly and progressively into competition mode."