ARSENE WENGER feels “convinced” his players can respond to their 4-0 Champions League defeat to Milan by beating Sunderland in today’s FA Cup tie but has been dealt a blow with the news that Per Mertesacker could be out for a long spell after having surgery on an ankle injury.

The Arsenal manager has pulled no punches since Wednesday’s humiliation at San Siro, which was the club’s heaviest defeat in Europe and a result Wenger described as a “disaster”, but he now insists it is time to move on and focus on gaining some success from this season.

“For us it is important not to dwell on that too much, focus on the next performance, respond in a positive way and ensure we have the mental qualities to be at this club,” Wenger said.

“We have put together a good series of results, we are in fourth position and we have an opportunity to qualify for the quarter-finals of the FA Cup. It is important that we are up for that and do not feel sorry for ourselves.”

Arsenal won at Sunderland in the Premier League a week ago but are no longer able to call on the man who scored the winning goal now that Thierry Henry has returned to New York Red Bulls.

Arsenal’s attacking options have been bolstered by the return of Gervinho from the Africa Cup of Nations but Mertesacker’s absence is a blow for a team who have kept one clean sheet in their past seven matches and are missing Laurent Koscielny after he injured his knee against Milan.

“Unfortunately he has had surgery and we have lost him for a while,” said Wenger of Mertesacker, who suffered ligament damage during the 2-1 win at Sunderland. “He had reconstruction, so it will be long term.”

Midfielder Lee Cattermole could be back in the Sunderland squad after recovering from a hamstring injury. Nicklas Bendtner is back in training but, as the Denmark striker is on loan from the Gunners, he is ineligible for the game at the Stadium of Light.