Radamel Falcao
Radamel Falcao has scored four goals since his summer arrival to Old TraffordGetty

Manchester United manager Louis van Gaal has admitted it is going to be difficult for under-fire striker Radamel Falcao to replicate his best form at Old Trafford and suggested Wayne Rooney will remain as the number nine for the game against Tottenham Hotspur on 15 March.

The Colombia international moved to the Premier League giants on deadline day in summer 2014 after agreeing a loan deal with Monaco, with the option of making the move permanent at the end of the season for around £44m ($65m).

Even though he missed much of the last campaign at Monaco due to a serious knee injury, Falcao arrived to Old Trafford with a high profile after garnering a reputation as one of the most prolific strikers around the world, both at Porto and Atletico Madrid.

However, Falcao has failed to replicate that form at Old Trafford, where he has only scored four Premier League goals in 17 appearances.

Van Gaal left him out of his starting line-up in the last Premier League game, against Newcastle United, and during the FA Cup defeat to Arsenal on 9 March, while the Colombian played on 10 March in the Under 21 side against Spurs.

And speaking during the press conference ahead of the Premier League game against Tottenham, the Dutch manager suggested the striker's future at the club complicated.

When asked why Falcao has not been the same player who was so lethal at Atletico Madrid, Van Gaal said, as reported by the BBC:" We are looking for the solution. Sometimes players can give fantastic performances in one country but not in another. It would not be the first time and it won't be the last."

Questioned whether the striker can recapture his form, the United manager admitted: "At a club like Man United it is more difficult. He has competitors. He knows Wayne Rooney is playing there and scoring."

Falcao 'humiliation' for playing in the Under 21 side

Nevertheless, in an interview with MUTV, the manager said the Colombia international will have a chance to play against Mauricio Pochettino's Spurs side and played down recent reports claiming it was humiliating for Falcao to play with the Under 21 side.

"I have 25 players and all of the players can play the next game," Van Gaal explained. "I have to maintain the rhythm of the game with every player. I have read about the 'big humiliation' for Falcao, but also Valdes was playing and Rafael as well. Michael Carrick has also played for the second team this season.

"That shows the professional attitude of the player but also the management of the club. It is not a humiliation, it is a professional attitude. In a training session, you never reach the intensity of 90 minutes. Of course, the second-team level is lower but that is also good that a player from the first team is playing much more minutes at a lower level, because then he can build up his confidence."

Speaking about Rafael, he added: "Of course I was impressed, and you could see in the training sessions afterwards that he had built up his confidence again and that is good for the players as well."