Arsene Wenger has expressed his concern after Aaron Ramsey limped out of Arsenal's 2-1 victory over Leicester, while the manger is unsure whether Alexis Sanchez will be fit enough for the Gunners' next game.
Ramsey, 24, came off the bench in the 73rd minute in Tuesday's Premier League clash at Emirates Stadium, but had to be replaced just nine minutes later.
When asked whether Ramsey had suffered a recurrence of his hamstring injury, Wenger is quoted by Arsenal's official website as saying: "It looks like it. I don't know how bad it is yet. Just visually, it didn't look good. When a guy stops straight away and sits down, that's not good news.
"There's a recurrence now of a few muscular injuries and it's difficult -- we haven't found out why. I basically left him out today because I wanted to be cautious with him. I had to bring him on -- I had a hesitation between [Mathieu] Flamini and him -- because we lacked a a bit of offensive power. It was not the best of decisions.
"Last year was a thigh but this year it's a recurrence of hamstrings. You cannot say it's no worry because after the player doesn't play with the freedom in mind."
On whether the midfielder will get an extended rest, he replied: "He's not overplayed. Before I never looked at him, I just played him in every game but since he's had these problems I'm a bit more cautious with him."
Sanchez, meanwhile, returned from an injury absence which saw him miss games against Aston Villa and Tottenham, but the Chile international was replaced 68 minutes in with Wenger similarly concerned over his fitness.
"Sanchez got a knock on his knee," Wenger said. "I don't think he was himself. From the moment he got this knock, he was never really comfortable. I don't know for how long he will be out and whether he will be out or not. I haven't seen the doctor.
"I was ready to take him off at half-time but he said, 'no it's OK, I can go on.' When I watched him play I thought, 'No, that hasn't [got better].' Sometimes when you run it off it's just a kick but he became worse and I didn't see him in the second half."
Wenger denied he was overly concerned with injuries affecting his first-team squad, adding: "No because for example [Mikel] Arteta has an ankle problem, [Mathieu] Debuchy and [Jack] Wilshere had an ankle problem and they are injuries you cannot do anything about.
"The only thing you can worry about are the muscular injuries. Arteta and Wilshere and [Theo] Walcott were joint injuries -- you cannot do anything about that. When you get tackles like we get, sometimes when the players are a bit tired it's difficult to get out of it."