Arsene Wenger admits England midfielder Jack Wilshere is an injury doubt ahead of Arsenal's Champions League clash at Barcelona on Tuesday.
Wilshere injured his ankle in the 0-0 home draw with Sunderland on Saturday and Gunners boss Wenger is yet to discover the full extent of the problem.
"Wilshere has an ankle problem," Wenger said. "We will see how he responds to treatment. He'll miss training tomorrow (Sunday). Maybe Monday he will be back."
With midfield duo Cesc Fabregas and Alex Song also struggling to be fit for the second leg tie at the Nou Camp when Arsenal will defend the 2-1 advantage established in the first meeting, Wilshere's injury couldn't have come at a worse time for Wenger.
Dutch striker Robin van Persie and England winger Theo Walcott are definitely out and Wenger's mood wasn't lifted by watching his side throw away the chance to significantly close the gap on Premier League leaders Manchester United.
If United beat Liverpool on Sunday they will be six points clear and Wenger was particularly incensed by referee Anthony Taylor's decision not to award a late penalty when Andrei Arshavin went down under a challenge from Titus Bramble.
The decision moments later when the Russian was incorrectly flagged offside after breaking clear of the visitors' defence.
"I'm too disgusted to speak about it," Wenger said. "These things can have an impact on the Premier League. Justice has not been done.
"I'm very happy with the performance. Defensively we were very good. We gave a lot physically.
"We lacked a bit of creativity, but we needed to be patient. What is frustrating is that we've given everything but we had a lack of sharpness in the final third and two decisions that went against us.
"They punished us severely, especially the offside that wasn't offside.
"If Arshavin had gone down, you would have said he had dived. I think he did right to stay up. You do not need to know that Bramble is beaten.
"You don't need to be a big specialist to realise that. My job is to deliver football game. The referee's job is to make the right decision."
The failure to take advantage of United's midweek slip at Chelsea came less than a week after Arsenal had lost to Birmingham in the League Cup final but Wenger insists he is happy with his side's current form.
"We have played now 11 games, eight wins and three draws," he said. "So we are quite consistent with our results.
"This result comes at a bad moment, I agree with you. Psychologically, will it have such an impact on the championship? I don't think so.
"We lacked sharpness and technical quality in the final third."
Sunderland manager Steve Bruce believes his side are now ready to move on from a recent dip in form and cited the return of substitute Danny Welbeck for his first appearance in two months as evidence his team is getting stronger.
"You can see when Danny came onto the pitch what we've been missing," Bruce said.
"We've been without a lot of players for months now so it's good to see a few of them back."
Bruce also hailed the performance of keeper Simon Mignolet, standing in for regular number one Craig Gordon, who will see a specialist in Sweden about a knee injury next week.
He said: "For me he has been a great find. He was playing in the Belgian league when we signed him.
"We are not surprised to see him produce a performance like that because we see it in training.
"But doing it out there is different. He's got the potential to be a fantastic young goalkeeper. He's got a big future."