Mauro Zarate has confirmed that he suffered a ruptured anterior cruciate ligament in Watford's 1-1 draw against West Ham on Saturday.
The former Hammers forward had been central to Watford's impressive start to the Premier League clash, winning the early penalty from which Troy Deeney scored.
However, having previously suffered a knock, Zarate went down in first-half stoppage time and was taken from the field on a stretcher after receiving lengthy treatment.
And he confirmed via Instagram the extent of his injury.
"Thank you everyone for your messages in this horrible moment," he wrote.
"With sadness I inform you that the results show the following: an anterior cruciate ligament rupture, plus a Grade 1 injury of the medial collateral ligament.
"I will face this with all my strength and will come back stronger than before."
Zarate was making just his third league appearance for Watford, having joined the club from Fiorentina in January.