Jurgen Klopp was dealt a huge blow at Vicarage Road on Monday night as star man Philippe Coutinho hobbled off in the opening stages of the game with injury.
The talismanic Brazilian has recently rediscovered his best form in a Liverpool shirt, scoring in four of the Reds' last five games.
But an early collision with Watford's Adrian Mariappa saw the No 10 clutching his leg with his face contorted in obvious pain.
The two players came together in a head-on collision, with Mariappa's knee catching the Brazilian high up on his right leg.