Manchester City have confirmed striker Gabriel Jesus suffered a medial collateral ligament injury during Sunday’s 0-0 draw at Crystal Palace.
The Brazilian, 20, went off in tears after injuring a knee during the first half at Selhurst Park.
City said the player would “undergo further examinations to establish the extent of his lay-off”.
City manager Pep Guardiola previously said the injury would keep Jesus out for “a little more than a month”.
Playmaker Kevin de Bruyne could also be set for a spell out after he left the field on a stretcher.
However, the Belgian was seen hobbling along the touchline after the game.
“You have to admire the physicality of the Premier League, but the referees need to protect the players, that is all I ask,” Guardiola said.
- Relive Sunday’s goalless draw at Selhurst Park
After arriving in January, Jesus missed two months of last season with a fractured metatarsal.
He is certain to miss Tuesday’s Premier League visit of Watford.
Jesus could be joined on the sidelines by De Bruyne, who has contributed a league-high nine assists this season.
The 26-year-old was on the receiving end of a late tackle from Palace midfielder Jason Puncheon.
“There is a line where you go above and it is dangerous,” said Guardiola.
“Sometimes because the football is quicker and faster it happens, they don’t want to hurt the other. But they can be out for a long time.”
The goalless draw ended City’s 18-match winning run in the Premier League, but they took a 14-point lead into 2018.
And they clung on to their unbeaten record in the league this season as goalkeeper Ederson saved Luka Milivojevic’s stoppage-time penalty after substitute Raheem Sterling had fouled Wilfried Zaha.
Sergio Aguero is their only fit senior striker, but Guardiola refused to confirm reports of a January move for Arsenal striker Alexis Sanchez.
“He is a player for Arsenal and I think he is going to stay there,” said Guardiola.
“In two days we have another game, after that we have meetings. My feeling now is Alexis is an Arsenal player.”
England defender John Stones was an unused substitute against Palace having been out for over a month with a hamstring injury.