Arsene Wenger admits that he is facing a "massive" challenge to salvage success from Arsenal's season.

The Gunners are in sixth place in the Premier League and seven points off the top four following Monday's 3-0 loss to Crystal Palace, although they have played a game less than fourth-place Manchester City.

The prospect of failing to qualify for the Champions League for the first time since Wenger became manager in 1996 has fuelled angry protests from some Arsenal fans, who have called for the club to replace 67-year-old.

Wenger concedes that his side is facing a tough task but he has called on his players to take risks in their performances in order to get the results they need.

"It's massive," he told a news conference when asked about the scale of the challenge. "We might get there, we might not but we have to believe we can do it. It's not the fear to fail, it's the desire to make it.

"It's a big challenge, of course. In football, you have to accept that you can win, lose or draw but you have to give everything to win the next game.

"It's not been very enjoyable but those moments are part of our job. You focus and prepare and make sure the next game doesn't go the same way.

"Playing with restriction doesn't help the performance. We are under pressure to deliver and the best way to play is to accept the risk."

Wenger confirmed that goalkeeper Petr Cech and centre-back Laurent Koscielny are in line to return for Monday's league meeting with Middlesbrough at the Riverside Stadium.

Cech has missed the last three league games after being forced off against West Brom with a calf problem, while Koscielny missed the matches with West Ham and Palace with an Achilles problem.

"We have a chance to get Petr Cech back in the squad and Laurent Koscielny is training. If the tests are positive then they will come back in the squad," Wenger said.

"[It's an] 80 per cent chance. At the moment it's pretty good but sometimes the 20 per cent plays the villain part in preparation."

Wenger added that David Ospina and Lucas Perez are still sidelined with respective muscle complaints.