• England forward has been out since end of April with knee injury • Alexis Sánchez in line to play against Crystal Palace

Arsène Wenger has expressed unease over the prolonged and complicated knee injury of Danny Welbeck. The England forward has been out of action since the end of April, and despite an initial diagnosis of a minor problem has missed 16 weeks and is not yet able to participate in full training. He is still restricted to gym work.

“It is much slower than expected,” the Arsenal manager said. “It was a bone bruising at the start. You think that it will be quite quick. He is an important player for us and the fact that he is not available is a bit of a concern.”

With the relationship between managers and medics currently so newsworthy, Wenger was asked whether the ongoing predicament was the fault of the doctors. “Maybe,” he said, chuckling. Joking apart, he is frustrated it is taking Welbeck, a deadline-day signing from Manchester United last summer, so long to regain fitness.

There is no sense that any kind of surgery is needed or would be particularly helpful. “That is what I have been told,” Wenger said. “It is bone bruising and nothing wrong at all. They have done all kinds of scans that today are very sophisticated and some of them I don’t understand at all. But they tell me no.”

Not for the first time for Arsenal in recent years, a player is suffering from an injury that is somewhat inexplicable. Wenger is thankful, therefore, to have a player on the other end of the fitness spectrum at his disposal in the seemingly super-powered Alexis Sánchez. The Chilean attacker is in contention to start Sunday’s game at Crystal Palace with Arsenal in dire need of a pick-me-up. After a short pre-season in the aftermath of the Copa América Sánchez is, according to Wenger, in reliable shape.

“He works extremely hard in every single training session to show that he is ready,” the Frenchman said. “It is what everybody should do. You wonder if he has created a beach at home and runs along the living room. He is a hyperactive guy. He needs that to be happy.

“He came back reasonably fit. He practised for two weeks before he came back. He did not start from zero.

“He is very ambitious, Alexis. He wants to win. He knows he won the FA Cup, he knows he won the Community Shield, he wants now to look to get more. And he is a winner.”

Wenger is mindful of Sánchez’s energy levels dipping at some point. “I am a bit worried but I knew before the start that once he is here, he would be difficult to stop. So I gave him a long enough break. He had four weeks off, which is quite reasonable.

“In March, April, May you could see he was a bit jaded. But he is still a guy who can be decisive in a game. Once he is out there he gives 100%. This season, he knows what is expected from him and he will do better than last year.”