Louis van Gaal has confirmed Manchester United striker Will Keane requires an operation for a groin injury he suffered during his side's 3-0 victory over Shrewsbury Town in the fifth round of the FA Cup. He has already missed the last two fixtures and the Red Devils manager confirmed the frontman will go under the knife as he joins the long list of injured players at Old Trafford.

Wayne Rooney last featured for the 20-time English champions in their 2-1 defeat to Sunderland and has been on the sidelines with a knee injury. Anthony Martial suffered a hamstring injury during the warm-up of the second leg Europa League tie against FC Midtjylland.

United host Watford in the league tie on 2 March and Van Gaal confirmed Martial and defender Matteo Darmian are available for selection. With the long list of injured players, the Red Devils boss confirmed he is struggling to rotate the squad due to key players spending more time in the club's treatment room.

"When I have choice enough, then I rotate [my squad]. There's no player in the English Premier League who can cope with the rhythm of matches. A player like Rooney could always cope but he is injured and not for the first time. So I have to rotate," Van Gaal explained, as reported by Goal.com.

"I have [Wayne] Rooney, I have Martial, I have [Marcus] Rashford, I had Will Keane but Keane is injured and will be operated on. When I have more players, I will rotate."

Keane, who returned from his loan spell with Preston, earlier expressed his disappointment after picking up the injury. The absence of Rooney, Martial and Keane forced the former Barcelona and Bayern Munich manager to start Marcus Rashford in the European competition and also in the Premier League fixture against Arsenal.

The teenage striker scored brace in those two fixtures and his form has impressed the Dutchman. It will be interesting to see whether Van Gaal will start with Rashford or will Martial take his place in the starting XI against Watford.