Manchester United skipper Wayne Rooney will have a scan on Wednesday to determine the damage to his injured knee, says boss Louis van Gaal.
Rooney, 29, missed Tuesday's 2-1 home win against Stoke after picking up the problem in the final moments of Saturday's victory against Hull.
"He will have a scan and then we will know more," said Van Gaal. "I hope the injury is not so serious."
He added that there is "more light in the tunnel" for United's injury list.
United have been hampered by injuries since Van Gaal replaced David Moyes in the summer, with the majority of his first-choice players missing matches at various stages of the season.
|Manchester United players injured this season|
|Goalkeeper: David De Gea||Midfielders: Angel Di Maria, Juan Mata, Michael Carrick, Daley Blind, Ashley Young, Ander Herrera, Antonio Valencia, Anderson, Marouane Fellaini, Jesse Lingard|
|Defenders: Rafael, Luke Shaw, Phil Jones, Marcos Rojo, Jonny Evans, Chris Smalling, Paddy McNair, Tom Thorpe||Forwards: Radamel Falcao, Wayne Rooney, Robin van Persie, James Wilson|
Asked if England forward Rooney was likely to recover in time for United's trip to Southampton on Monday, Van Gaal added: "I don't think so, but you never know."
The United boss also expects to be without Di Maria at St Mary's, where his fourth-placed side target their fifth-straight Premier League win.
United's 26-year-old record signing, who joined from Real Madrid for £59.7m in the summer, was substituted after just 13 minutes against Hull with a hamstring strain.
"Di Maria is not so serious, but he won't play against Southampton," said Van Gaal. "But we've got more players coming back and we can see a little more light in the tunnel."