Arsenal midfielder Aaron Ramsey ruled out for three weeks... but Arsene Wenger insists he does not regret letting Jack Wilshere leave on loan

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Aaron Ramsey is set to miss a potentially season-defining period for Arsenal after the Welshman was ruled out for three weeks with a calf strain.

The 26-year-old was substituted just 20 minutes into the Gunners' shock home defeat by Watford on Tuesday night and will now miss Saturday's crunch Premier League clash with Chelsea, as well as the first leg of the Champions League tie with Bayern Munich.

His absence leaves Arsenal short in midfield for a crucial period, which also includes a league date with Hull and a trip to non-league Sutton in the FA Cup, at a time when Granit Xhaka is suspended, Santi Cazorla is injured and Mohamed Elneny is away on Africa Cup of Nations duty with Egypt.

Arsenal midfielder Aaron Ramsey has been ruled out for three weeks with a calf injury

Arsene Wenger revealed the news at his press conference ahead of the game at Chelsea

Alex Oxlade-Chamberlian is set to be involved against Antonio Conte's side despite facing a fitness test, with Wenger confident the likes of Ainsley Maitland-Niles can deputise after a strong display against Southampton in the FA Cup.

But at a time when he is thin in midfield, Wenger does not regret allowing England international Jack Wilshere to spend the season on loan at Bournemouth. 

'Overall from the other night we lose Aaron Ramsey, he is expected to be out for 21 days,' Wenger said.

Ramsey is set to miss vital games in the Premier League, FA Cup and Champions League

'We are a bit short at the moment but I think we have young players who can do well in there, we have Jeff Reine-Adelaide and Maitland-Niles, Chamberlain and Iwobi can play in there so we still have some strengths.

'No (regrets) we agreed for him (Wilshere) to go on loan for a year and we accept that. When you consider the whole of the year I would like to reiterate to him we didn't push him out. He wanted to go somewhere and play and we agreed with that.

'I accepted to let him go and we have to deal with the consequences of that.'

Wenger knows his side now face a vital period with three games in league, cup and European competitions, but insisted such spells come with the territory for teams looking to win trophies.  

Despite being short of options in midfield, Wenger does not regret loaning Jack Wilshere out

He said: 'Yes but that's competition. When you accept competition and want to be at the highest level you have to accept you have defining moments and games.

'We have accepted this job and the beauty of it is that you can have highs. First of all we want to recover from this disappointment and the team is healthy and united. We're all focussed on tomorrow's game.' 

Wenger also expects Olivier Giroud and Danny Welbeck to be ready to face the Premier League leaders at Stamford Bridge.