Manchester United boss Jose Mourinho admits Ander Herrera could be missing for six weeks.
For Sunday's clash with Chelsea, Herrera was ruled out of with the hamstring strain he suffered in the goalless draw against Sevilla in midweek.
The midfielder could be out for some time while Phil Jones, Marcos Rojo and Marouane Fellaini remain sidelined.
"Ander is out," said Mourinho. "I don't know the final diagnosis but I know he is out for a few weeks. I don't know how to say 'few' – two, three four, five or six. I don't know. Coming back from injuries? Nobody else."