Monaco's Radamel Falcao (R) celebrates after scoring against Nantes during their French Ligue 1 soccer match at the Beaujoire in Nantes, Aug 24, 2014. [Photo/Agencies]

LONDON?- Manchester United signed Radamel Falcao on loan from Monaco early Tuesday in a coup by the struggling club on the final day of the summer transfer window.

The record 20-time English champions are paying around $9 million to Monaco to take Falco on loan for the season with an option to buy the 28-year-old Colombia striker.

Bringing one of the hottest properties in world soccer to Old Trafford was a surprise move by United's owners, with the Glazer family under pressure to spend after a rapid decline since Alex Ferguson retired as manager in May 2013 after more than 26 years in charge.

"Manchester United is the biggest club in the world and is clearly determined to get back to the top," Falcao said in a statement. "I am looking forward to working with Louis van Gaal and contributing to the team's success at this very exciting period in the club's history."

United's need for reinforcements has been highlighted by the failure to win any of its opening four matches under Van Gaal, who was hired to halt the slump under David Moyes last season. United's latest setback was a 0-0 draw at Burnley on Saturday, following a humiliating League Cup loss to third-tier club MK Dons.

Falcao only joined Monaco from Atletico Madrid last year in a deal worth 60 million euros (then $78 million), but missed the second half of the season through injury. At Atletico, Falcao scored 70 goals in 91 appearances, and before then netted 72 in 87 Porto games.

"He is one of the most prolific goalscorers in the game," Van Gaal said. "His appearance-to-goal ratio speaks for itself and when a player of this caliber becomes available it is an opportunity not to be missed."

United, which is listed on the New York Stock Exchange, has spent around $250 million on players since finishing seventh last season, with Argentina midfielder Angel Di Maria joining last week for a British-record fee of 59.7 million pounds (then $99 million). Versatile Netherlands international Daley Blind completed his move from Ajax for 14 million pounds ($23 million) on Monday as Falaco's deal was being seal.

In Van Gaal's 3-5-2 system, Falcao could partner Robin van Persie up front, with captain Wayne Rooney dropping into midfield and assuming the No 10 role. Those tactics could put Juan Mata's starting place at risk after he arrived in January for 37.1 million pounds (then $61 million).

Falcao is leaving a club he helped to qualify for the Champions League for one not participating in any European competitions this season.

Monaco owner Dmitry Rybolovlev, a Russian billionaire, spent heavily to establish the team as a footballing power after winning the second division title in 2013, with Falcao the marquee recruit. But Falcao's season - and World Cup hopes - were ended following left knee surgery in January and Monaco was beaten to the title by Paris Saint-Germain.

Colombia striker James Rodriguez, who was the top scorer at the World Cup, has already been sold to Real Madrid after just a year on the French Riviera. Losing Falcao is a further blow to Monaco's ambitions and leaves the club with veteran forward Dimitar Berbatov as the club's best option in attack.

The signings of Falcao and Rodriguez were meant to herald a new era for Monaco, one where they could challenge big-spending PSG. But losing such big names deals a significant blow to the club's prospects of competing at the highest level.

"I am sorry to our supporters for the departure of Radamel Falcao," Monaco vice-president Vadim Vasilyev said. "But we felt that once the player had expressed his desire to join Manchester United, we couldn't stop him. It interesting to see that the biggest clubs want our players."

Falcao is leaving a club that attracted less than 10,000 fans at its weekend game for a club which usually sells out the 76,000-capacity Old Trafford.