LONDON (AP):

Manchester United signed Radamel Falcao on loan from Monaco yesterday 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 US$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 football 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.

While Manchester United were signing Falcao Arsenal bolstered their attacking options by signing Danny Welbeck from the former Premier League champions.

The England forward joined the London club for a reported US$27 million as the summer transfer window was closing yesterday.

The need for Arsene Wenger to sign a striker came after Olivier Giroud was ruled out until at least the end of December with a broken left leg.

"Manchester United are the biggest club in the world and are 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 their 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 US$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 calibre becomes available it is an opportunity not to be missed."

United have 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 US$99 million.

Versatile Netherlands international Daley Blind completed his move from Ajax for US$23 million yesterday as Falaco's deal was being sealed.

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 US$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.

"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.