The 23-year-old was forced off the field in the first half of Wednesday's 2-2 draw with Liverpool after suffering a thigh strain.

Wenger has confirmed that the injury will necessitate a long-term lay-off.

"It will be four to six weeks (out)," he told reporters on Friday.

While disappointed with losing Gibbs, Wenger was delighted after the club completed the signing of left-back Nacho Monreal from Malaga on deadline day.

The 26-year-old agreed a long-term contract with the Gunners on Thursday to become their sole addition of the January transfer window.

The Frenchman said Monreal could be set for a debut at the weekend in the Premier League clash against Stoke at the Emirates Stadium.

"I believe Gibbs will be out for the Champions League. Santos could have a key role," the 63-year-old said.

Wenger strongly defended Santos, who has come in for criticism during a recent poor run of form.

"Santos is the type of player who gets sharper from competition. Yes (some criticism he gets is unfair)," he said.

"I believe we need two left backs. We had two before, we have two again now because Gibbs is out."

He added: "Monreal is available for the weekend game. Yes (he can improve our defence) but we want him to take part in our collective play.

"He can play as a left winger too and he can adapt very quickly."

Monreal said he believed he was a perfect fit for Arsenal's passing game style.

"Arsenal like to keep the ball, which is beneficial for me," he said.

"And I like this part of the team's game. I love playing with the ball at my feet - short, sharp touches and good movement.

"I think Arsenal do have certain elements of Spanish football philosophy.

"The Spanish people know there are some great players of great quality in this team and I hope that we can play good football."

Meanwhile, Wenger joked that David Beckham's deadline-day move to Paris Saint-Germain is testament to how good Arsenal training sessions are.

The former England captain was training with the Gunners to keep himself match fit ahead of his completed move to PSG on Thursday.

"It just shows how effective our training is! He trained here once and is bought by PSG," he said.

Wenger had earlier ruled out a move for the 37-year-old insisting there was 'no speculation' linking him with a move to the London club.

Beckham revealed he had turned down offers to come back to the Premier League as a direct result of his loyalty to Manchester United whom he left in 2003.

"I've been successful with Manchester United and have always said I would never want to play for another English club," he said.

"I've a lot of history with Manchester United. They were the team I supported and dreamed of playing for. I couldn't do it."

The former LA Galaxy midfielder has signed a five-month contract with the Ligue 1 club and will donate all of his 150,000-pound wages to a children's charity located in Paris.

The move will also see him joining up with coach Carlo Ancelotti whom Beckham played under during his loan spell with AC Milan.