Arsenal manager Arsene Wenger has confirmed both Aaron Ramsey and Alexis Sanchez suffered fresh injuries during the 2-1 victory over Leicester City.
Sanchez, who had missed the club's last two games against Aston Villa and Tottenham Hotspur, started the match at the Emirates Stadium on Tuesday 10 Feburary but came off in the 68th minute with a knock to the knee.
"Sanchez got a knock on his knee. 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," Wenger told a post-match press conference.
"I was ready to take him off at half-time but he said, 'no it's okay, 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."
Wales international Ramsey came on with 15 minutes of the match remaining, replacing Theo Walcott, but just ten minutes later was forced off again and was replaced by Mathieu Flamini after suffering a fresh problem.
Asked whether Ramsey's injury was another hamstring problem, Wenger said: "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," he said.
"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 Flamini and him - because we lacked a a bit of offensive power. It was not the best of decisions."
The north London side put their weekend defeat at Tottenham behind them with a nervous victory over the Premier League's bottom club to climb into the Champions League places.
Arsenal looked on the way to securing an easy victory after Laurent Koscielny and Theo Walcott scored before half-time.
However, Andrej Kramaric's goal early in the second-half saw Leicester pushing for the draw until the very last minute.
"I feel that we were in control for the first half but when we were in control they had one or two good chances on the counter-attack. In the second half we lost our cohesion, our technical superiority and Leicester was always dangerous going forward," Wenger said.
"They are very quick in transition from defence into attack. At 2-1 we became a bit nervous but overall what was important for us was to get the three points."