Birmingham City midfielder Borja Oubina faces at least six months on the sidelines after rupturing his cruciate ligaments.
The Spaniard underwent medical tests, which confirmed the damage to his left knee, over the weekend and he has admitted his disappointment.
He said: "This is terrible because I arrived in the Premier League with much anticipation.
"I wanted to demonstrate that I would be able to play in this competition. From the first moment I noticed the injury I feared for the worse."
Oubina, who has two caps for Spain, suffered the same injury to his right knee in 1997.
