Manchester United will reportedly try and sign Barcelona midfielder Alex Song if their big-money transfer for Juventus' Arturo Vidal collapses.

The Red Devils have opened negotiations with Juve over a deal for the Chile star for a fee thought to be about £45million - with the Italian champions having told United that they have one week to wrap up a transfer for the 27-year-old, according to The Daily Express.

However, United manager Louis van Gaal is believed to be concerned about Vidal's fitness following the midfielder's history with ankle and knee injuries in the past.

Despite the Chilean having undergone an initial assessment by United doctors recently, it is now thought that Van Gaal has already earmarked former Arsenal midfielder Song should United's proposed move for Vidal fall through.

Song has failed to make a mark in Spain since moving to Barcelona from The Gunners in 2012, and Luis Enrique is believed to be ready to offload the Cameroon international this summer should any suitable bids for the 26-year-old arrive.

The player has also been targeted by Tottenham Hotspur in recent weeks, but, Song would reportedly prefer a move to United if he leaves Barca this summer.