Watford's Mauro Zarate suffered an anterior cruciate ligament injury against West Ham United on Saturday.
Zarate, a January signing from Fiorentina, twisted his knee awkwardly towards the end of the first half of the 1-1 draw against his former club.
The winger needed oxygen and nine minutes of treatment on the pitch before being carried off on a stretcher and taken to hospital for scans.
And on Sunday the 29-year-old revealed the extent of the damage in an Instagram post.
He wrote: "With sadness I inform you that the results show the following: anterior cruciate ligament rupture plus an injury grade 1 of medial collateral ligament.
"I will face this with all my strength and will be back stronger than before."
A post shared by Mauro Zarate �������� (@maurozarate20) on
Zarate was making only his third appearance for the Hornets and earned the penalty from which Troy Deeney opened the scoring, but he now faces a lengthy spell on the sidelines.