Arsenal in the dark over Tomas Rosicky return... as Jens Lehmann backs Petr Cech to come good after 'cruel' debut

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Manager Arsene Wenger admits Arsenal do not know how long Tomas Rosicky will be sidelined for following knee surgery, but revealed midfielder Jack Wilshere was on schedule with his recovery from a hairline fracture in his ankle.

Rosicky, who agreed a contract extension at the end of last season, has been struggling with a knee problem since June following international duty with the Czech Republic, and is set for another lengthy spell of rehabilitation.

Wenger suggested the club were reluctant to place any specific time frame on the recovery of the 34-year-old, who has endured a string of fitness issues over his Arsenal career.

Tomas Rosicky is set for another lengthy spell on the sidelines following knee surgery

Arsene Wenger has admitted he doesn't know how long it will be before the Czech playmaker returns

'Tomas has had surgery on his knee. His agent said he will be out for one or two months, but it will be longer. How long exactly, we don't know yet,' Wenger confirmed to the club's official website.

The prognosis on Wilshere, however, is more positive.

The England international had impressed during the pre-season trip to Singapore and in the Emirates Cup, but picked up another frustrating injury on the eve of the FA Community Shield against Chelsea at Wembley.

Wilshere is understood to have been recuperating in Dubai to help aid his natural healing process.

Wenger added: 'We said Jack would be out for four weeks, and he's in the second week now so he's on schedule.'

Jack Wilshere's recovery from a hairline fracture of his ankle is reportedly 'on schedule'

Copa America winner Alexis Sanchez made a sooner than expected return against West Ham

Arsenal should have full-back Hector Bellerin available again for the trip to Crystal Palace on Sunday after sitting out the 2-0 home defeat by West Ham, but while Wenger says forward Danny Welbeck is 'making good progress' from a knee problem, he is not expected to feature.

A surprise inclusion on the bench against West Ham was Alexis Sanchez, who had just returned to training following an extended break after helping Chile win the Copa America.

Wenger revealed the tenacious forward was keen to get back into action again.

He said: 'Alexis Sanchez is fit, he's been working hard and is ready for the weekend.'

Arsenal continue to be linked with a big-money move for Real Madrid forward Karim Benzema, but following the disappointment of defeat to West Ham, when summer signing Petr Cech endured a nightmare debut, Wenger maintained the immediate resolution must come from within.

New arrival Petr Cech had a debut to forget in Arsenal's opening day Premier League defeat by West Ham

The former Chelsea stopper was arguably at fault for both of the Hammers' goals at the Emirates

'I knew we had a very difficult schedule from the start and that is why we have to be on our toes very quickly and respond very well now,' Wenger said to Arsenal Player.

Meanwhile, former Arsenal No 1 Jens Lehmann has backed Petr Cech to have a 'fantastic season', despite his struggling debut against the Hammers.

The former Chelsea keeper arguably at fault for both goals in the 2-0 opening day defeat at the Emirates after being hailed as the signing to turn the Gunners into serious title contenders.

Lehmann, a member of the 'Invincibles' squad who claimed Arsenal's last league title in 2003/2004, believes the 33-year-old will be motivated by what he described as a 'cruel' introduction.

Jens Lehmann,  who won the title with Arsenal in 2003/04, has backed Cech to have a 'fantastic' season

'I expected him to be really good from the beginning,' said the German.

'But sometimes it takes a while to adapt to a new club, particularly when you are coming from a major rival like Chelsea. It takes time.

'On the other hand, Chelsea disappointed him because he couldn't play there last season.

'He has seen the cruelty in football -- you are a hero one year and the next year you are not even playing any more. That could spur him on to play a fantastic season for Arsenal,' he added.