Ander Herrera
Herrera went off late into United's 2-1 win over West Ham (Getty Images/Laurence Griffiths)

Manchester United's injury crisis has continued with the news that midfielder Ander Herrera has been ruled out for an indefinite period with a cracked rib suffered against West Ham United.

The Spaniard was replaced by Antonio Valencia after 74 minutes of United's 2-1 win over the Hammers initially with a back complaint, with manager Louis van Gaal refusing to address the full extent of the injury over the weekend.

Herrera had attempted to calm fears over his long-term fitness by stating he hoped the problem would heal in time for the Premier League visit of Everton, but United have confirmed their summer signing from Athletic Bilbao faces a lengthy spell on the sidelines.

Ander Herrera
Herrera was hopeful of a speedy recovery over the weekend. Facebook/anderherrera

A club statement read: "Manchester United midfielder Ander Herrera sustained a fractured rib during the match against West Ham United on Saturday.The club will continue to monitor his progress over the next few weeks."

The 25-year-old, who has scored two goals in four appearances during an impressive start to his Old Trafford career, becomes the latest high-profile injury victim for United and leaves the club without nine first team players for the game against Everton prior to the international break.

Defenders Jonny Evans, Chris Smalling, Phil Jones and Jesse Lingard are all out while midfielders Michael Carrick, Marouane Fellaini and Ashley Young are also absent. Wayne Rooney's sending off against West Ham means he will be unavailable until November.

The crisis has swelled a harrowing start to Van Gaal's reign at United, which has been dogged by injury problems, lack of form and a run of just two wins in his first seven games in charge.

On United's recent problems with injury, Van Gaal said last week: "I have been told [about this] and now they are confirming [it]. But I have good hopes that we shall improve in that matter because normally I don't have any injuries.

"As a good example, for a player who was many times injured – [Arjen] Robben – he was never injured [during my reign]."

"[I hope to ensure the injuries stop] by training. By training sessions and adapting to their level. It was not only Robben but every player.

"And we are doing that here in the same way, only less than I have done with Bayern Munich. We have to improve the level and intensity so players can play the game."