MANCHESTER -- Ilkay Gundogan could be out for the rest of the season after the Manchester City midfielder damaged his cruciate knee ligaments earlier this week.
Gundogan, 26, left the pitch in tears after damaging his knee in Wednesday night's 2-0 victory over Watford.
The Germany international will have an operation on the injury, which is expected to keep him out for at least six months.
Gundogan was Pep Guardiola's first signing at the club and was becoming an integral part of the City midfield, having started 15 of 20 matches since recovering from a dislocated knee that ruled him out of the European Championship and City's preseason.
"He will be out for a long time," Pep Guardiola told a news conference ahead of City's game with Arsenal on Sunday. "It's so, so difficult for him. We are sad for him. We are going to miss him a lot. It's what it is. He's unlucky, sometimes football happens.
"He's sad, we are sad, he is upset. It happened in action when the opponent was correct, he went to fight and it was an unlucky situation. Sometimes there are moments when the opposition go harder but it was a normal situation.
"Now we need him to feel we are there and wait and come back safe. He's going to be operated and be back as soon as possible.
"During the season sometimes it happens. This kind of situation happens. We are going to miss but now we will support him. I am sure he is sad but he will have an operation, then come here and see his teammates."
City paid Borussia Dortmund £21 million for Gundogan despite him still recovering from a knee injury picked up in May. He also missed 15 months of his career with a serious back injury.
The injury leaves Guardiola short in midfield, although he says he Yaya Toure is back to his best after being frozen out at the start of the season for comments from his agent.
"Now [Toure] has come back. I have seen him play like he can and was when I met him in Barcelona," Guardiola said. "He's a player with no doubt about his quality.
"Of course we have other options. We have Fernando, Aleix [Garcia], Kevin [De Bruyne] can play in that position as well. We have a lot of options. In the next game Fernandinho is coming back.
"During the season these things happen. You don't expect to be all season with all the players fit. But we want the injuries as short as possible and in Ilkay's case is that not going to happen."