Pep Guardiola believes a lack of rest may have contributed to the knee injury of Kevin de Bruyne.

De Bruyne will be out three months but won't need surgery.

"Like the doctor said, it will be two to three months, hopefully he can do as much as possible to get back and help us again," Guardiola told a news conference.

"It will be a big miss like last season with Benjamin Mendy. Last season Kevin was outstanding in all terms and of course for him and his family you never want this but you accept it's part of the game.

"It's especially part of the game for the players -- it's normal, they don't rest. It's a tough season, short recovery, they say let's go and we are in the competition. Human beings have a limit and sometimes these things happen."

Kevin De Bruyne has suffered a right knee injury in training on Wednesday and is undergoing tests to determine the severity.

De Bruyne is expected to fly to Barcelona for further tests with specialist Dr. Ramon Cugat who treated him when suffered a knee injury in January 2016.

De Bruyne only returned to training last Monday after helping Belgium to the semifinals of the World Cup in Russia. De Bruyne was a second-half substitute in the 2-0 Premier League-opening victory over Arsenal on Sunday, coming on in the 60th minute.