Manchester United can send Radamel Falcao straight back to Monaco if he has a recurrence of the knee injury that threatened to wreck his Old Trafford move. The 28-year-old Colombian striker tore the anterior cruciate ligament in his knee playing for Monaco in the French Cup in January.

He was forced to withdraw from the World Cup after undergoing surgery and doubts continued to persist whether he would ever reclaim the form that made him one of the most prolific strikers in the game.

When United signed him on loan on transfer-deadline day with a view to completing a near £50m permanent transfer they put Falcao through a vigorous medical to safeguard their investment and test the knee.