The Red Devils completed a reported £52m deal to sign the Brazil international from Ukrainian Premier League champions Shakhtar Donetsk.
Fred has been signed to improving Jose Mourinho’s options in the middle of the park following Michael Carrick’s retirement at the end of the 2017-18 season.
The South American star will also complement holding midfielder Nemanja Matic and club record signing Paul Pogba in the heart of Mourinho’s team.
Fred won three Ukrainian Premier League titles during his spell at Shakhtar as well as helping the club to reach the Champions League knockout stage twice.
Former FC Barcelona and Brazil star Rivaldo raved about the new Manchester United signing following his lucrative move.
“He is a wonderful player,” Rivaldo told Sky Sports.
“Like any other player when you move to a new country, he will need a little bit of time to adapt.
“But when you are a good player and a brilliant midfielder like he is, he is going to do well and he is going to be good for Manchester United and they will be good for him.”
Fred scored 14 times in 156 games in all competitions during his five seasons at the Ukrainian club.
Manchester United haven’t won the Premier League title since 2013 when Sir Alex Ferguson was still in charge.
The Red Devils finished in second place in the Premier League table last term ahead of Tottenham Hotspur and Liverpool FC.
Manchester United lost 1-0 to Chelsea FC in the FA Cup final at Wembley last month.
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