Danny Welbeck suffered a "significant" right ankle injury during a match Thursday in the League against Sporting Lisbon, his Arsenal club said.
A 27-year-old English international player was shot on stretchers in an unsuccessful draw at Emirates Stadium.
Welbeck, who was injured when he jumped on his head and landed poorly on his right ankle, remains in the hospital and will continue to be judged.
"The next update will be released in the next 72 hours," the club said.
Several of Welbeck's friends looked desperate when he was treated long and needed an oxygen mask.
Arsenal manager Unai Emery said: "He worked well and had a good match, and he also had some chances, his injury was with the mentality of the players."
Welbeck, who scored 16 times in 42 international appearances, was named in England's last team for upcoming matches against the United States and Croatia.
He has five goals from 14 games for Shooters this season.