كتب : Hatem Maher
"The 35-year-old will arrive on 1 January and will remain at Old Trafford until 12 March," United said in a statement on their official website.
United boss Alex Ferguson said he is delighted to acquire the services of the former Barcelona and Celtic man, while admitting that the club have made previous enquires about his availability.
"I have always admired him. I made a move for him when he was at Celtic, but then they managed to persuade him to stay," the Scottish tactician revealed.
"He is a great player. It is a terrific bit of business for us. We are bringing someone in who can change a game."
Larsson is expected to serve as a back-up to regular starters French international Louis Saha and England's Wayne Rooney.
"I will go over there to play as much as possible - but I have no idea of how Ferguson wants to use me. Am I a back-up?" Larsson said.
"Yes, at the beginning; I probably won't play every match from the start. But then you will see what I can contribute and how things are going."
The former Sweden international sparkled during his seven-year spell with Scotland's Celtic before joining Barcelona in 2004.
He played a key role in helping the Catalans clinch the UEFA Champions League trophy when he came on as a substitute in the final against Arsenal to produce two assists as Barcelona came back from behind to earn 2-1 victory.