Arsène Wenger has suggested that Arsenal's injury problems might be related to his players taking legal supplements to enhance aspects of their lifestyle and performance without the knowledge of the club.

The manager revealed last month that he had ordered an investigation into the club's training methods and medical procedures in an effort to establish whether they could have avoided their latest injury crisis. The absence of the attacking midfielders Aaron Ramsey, Theo Walcott, Mesut Özil and Jack Wilshere has hit them hard while the defender Laurent Koscielny has also been out with a muscle strain.

Arsenal's Premier League title challenge appears to have been overtaken by the more familiar battle to finish in the top-four and trip to fifth-placed Everton has assumed tremendous importance. The good news for Arsenal is that Ramsey will return to the squad after more than three months out with thigh trouble, although he will feature as a substitute at best while the full-back Nacho Monreal is also back in contention after a foot injury.

Wenger said that the internal review had yet to yield any hard and fast conclusions but he advanced a personal theory. "Some of them [muscle injuries] are down to the medication that the players take that you don't even know about. Then you realise afterwards that they took this medication but that's not prudent."

He added that certain medication could affect the liver and then it "doesn't work as well ... the toxins don't go as quickly out of the body as they should and they [the players] get tired". Injuries are sometimes the result of lower levels of stamina; if a player is, to borrow a phrase from Wenger "in the red".

He was asked to give examples of the kind of medication he was referring to. "If you lose your hair and you've taken something to make your hair grow, it might not be good, especially for the rest of your body," he said. "Medication always pushes a part of your body and is sometimes detrimental to other parts of your body.

"At the moment, we have not come to any conclusion … every case can be very different and you need to analyse very deeply why things happen. I'm surrounded by people who want to enhance their performances because they have another problem in their life and it's not always necessarily a good thing to do."

Arsenal's doctors do not believe that there is a link between supplements, tablets or medication and injuries while no one in the squad is on long-term medication. The doctors strive to provide and oversee the use of any supplements that may be required.

Ramsey was in the red before he played at West Ham United on Boxing Day, the league fixture in which he suffered his thigh injury but Wenger admitted that because the player was in the form of his life, he had struggled to give him a rest. "When Ramsey got his injury we saw he was tired at West Ham, so maybe sometimes when the player is very important as well, you are tempted to play him even when he is tired," he said.

Ramsey's performances over the first-half of the season had advertised him as a potential player of the year and although that chance has gone, there remains plenty for him and the team to play for, not least the FA Cup, in which they face Wigan Athletic in the semi-finals next Saturday. "The number of goals Ramsey has scored is tremendous for a midfielder," Wenger said. "He turns up in the box. He is a bit Lampard-ish. There is a lot more to come from him."