Radamel Falcao
Radamel Falcao has scored just four goals for Manchester United this seasonGetty Images

Former Arsenal midfielder Paul Merson has urged Jose Mourinho to sign Manchester United striker Radamel Falcao as a backup for Diego Costa.

The Colombian international is on a season-long loan and since making a switch to Old Trafford, he has struggled to regain his form he showcased for Atletico Madrid and FC Porto. He has started in only 13 league games and scored four goals and managed four assists this term.

Costa has struggled with injuries, despite finding the back of the net regularly for the Premier League leaders. His injuries have left the Portuguese tactician with Loic Remy and veteran Didier Drogba as the other two strikers.

Merson believes Falcao can regain his form if he gets a good run of games, something that he has failed to secure under Louis van Gaal.

"Watching that [Falcao's performance for United at Stamford Bridge] last week, I think Chelsea would take him at £15million – they need another centre forward," Merson told Sky Sports.

"Whatever happens next season, to be successful in the Premier League and in Europe, they need another centre forward badly, because when Costa hasn't played they've missed him."

"If he went down to £15m then I think there would be a lorry load of teams after him. He is a good player and I think he'll get fitter and fitter.

"He hasn't really had a season; he has only been in and out. He needs to play 20 games and then I think he'll be back to where was when, for me, he was one of the best centre forwards in world football," he added.

Drogba's contract will expire at the end of the season and the Ivorian has already expressed to play for one more year. It should be seen whether the former Real Madrid boss will hand him a new contract.

Mourinho will be looking to sign a striker in the summer transfer window. The Blues were interested in signing Falcao, while he was at Atletico. Meanwhile, Van Gaal has hinted that the Colombian striker could still be at United next season.