Manchester City goalkeeper Ederson could be out for the rest of the Premier League season.
The shot stopper faces a serious race against time to make the FA Cup final as well.
Ederson suffered a knock during the team's 2-0 win over Nottingham Forest, coming off at half time.
It doesn't look good," said Guardiola, when asked about Ederson by reporters post-game.
We'll see tomorrow with the doctor."
On the game, he added: "It was more than hard. Such a difficult game, but we knew that. It's always difficult to come here. We suffered a lot but, in the end, we'll take it.
"The pressure is about how you play. iIf you play well and control the game, then people say you don't feel the pressure. If you play badly, people say you feel the pressure.
"We were lucky today that the pitch was so dry, because that was the reason they missed the chances they did. We were lucky the pitch was in this condition."