Marcos Rojo
The Argentine defender dislocated the shoulder during a training session last week.Getty

Manchester United's injury woes have gone from bad to worse, with Marcos Rojo revealing he has been forced to undergo surgery to deal with shoulder problems. The Argentina defender said the operation had been successful, but the news is a fresh blow for Louis van Gaal after Matteo Darmian and Chris Smalling joined the busy treatment room following Champions League elimination at the hands of Wolfsburg.

Van Gaal revealed last week that Rojo would be unavailable for the Premier League tie against West Ham United after dislocated his shoulder during training. The Dutch boss refused to set a schedule for the player's recovery, but reports suggested the Argentine would be out for a number of weeks after falling victim a similar injury against Manchester City last season.

"It was already in the media – Rojo has been injured," Van Gaal said ahead the game with the Hammers. "It's his shoulder, the same as last year, in a training session. It's very unfortunate, it's the position of Luke Shaw so I have a great problem."

Rojo has now revealed he has been forced to go under the knife – an action that was not taken last year. He refused to clarify his expected time out.

"My operation was a success," he wrote on Instagram. "Thank you to my beautiful wife, always with me. Thank you everyone for your messages of love and support."

The news comes just one day after Darmian and Smalling joined Phil Jones, Luke Shaw and Antonio Valencia in Van Gaal's defensive injury list ahead of the game against Bournemouth. Ander Herrera, Morgan Schneiderlin and Wayne Rooney may be also out after the trio missed the Champions League defeat against Wolfsburg.