Watford forward Mauro Zarate faces a lengthy spell on the sidelines after injuring his cruciate ligament during Saturday's 1-1 draw with West Ham.
The 29-year-old was taken off on a stretcher in his third appearance since joining from Fiorentina in January.
In an Instagram post, Zarate said scans revealed an "anterior cruciate ligament rupture plus an injury grade one of [the] medial collateral ligament".
The typical recovery period for a cruciate ligament injury is six months.
However, it can be longer if surgery is required on the knee.
"Thank you everyone for all the messages in this horrible moment," former West Ham and QPR striker Zarate added.
"I will face this with all my strength and will be back stronger than before."
Watford are 12th in the Premier League with 12 matches remaining.