LONDON (AFP) - Alex Ferguson saluted Ryan Giggs' "fantastic career" after the Manchester United icon announced his retirement to concentrate on his new role as assistant to Manchester United manager Louis Van Gaal.

Former United manager Ferguson signed Giggs on his 17th birthday in 1990 and saw him become the most decorated player in the club's illustrious history.

The Welsh midfielder is well established as one of European football's all-time greats after making 963 appearances for United, scoring 168 goals, and winning 13 Premier League titles, four FA Cups, four League Cups and two Champions Leagues.

And Ferguson, who retired at the end of the 2012-13 season, was quick to pay tribute to the 40-year-old in a video message on United's official website: "What a fantastic career - the number of games you have played, the trophies you have won, the help you have given young people and the help you have given me and all the coaching staff."

Former United midfielder David Beckham, who emerged from the Old Trafford youth academy at the same time as Giggs, paid tribute to his team-mate's remarkable loyalty and longevity.

"Amazing servant to the game of course, but more importantly, an amazing servant to Manchester United," he said. "We are all proud of you - Manchester United fans love you."

Giggs, who finished this season as United's interim manager for four matches following David Moyes' sacking, will now concentrate on assisting Dutch coach van Gaal, whose appointment at Old Trafford was confirmed on Monday.

Gary Neville, another of Giggs' former youth team and first team colleagues at United, said he doubted whether the star's trophy haul would ever be beaten.

"Well done for everything you have achieved at the club," Neville said.

"It is wonderful what you have done and I don't think your achievements will ever be surpassed."