Cambridge United midfielder Issa Diallo has suffered a ruptured Achilles tendon and will be out for several months.
The 27-year-old came off in last week's loss at Wycombe, but it was hoped the injury would not be too severe.
He had featured eight times for the U's in League Two this season.
"Diallo has unfortunately ruptured his Achilles, which is unbelievable when you consider how innocuous it looked at the time," boss Richard Money told BBC Radio Cambridgeshire.
Without Diallo, Cambridge won 3-1 at top-of-the-table Burton on Friday.