The Red Devils announced that they had agreed a deal to sign the Brazilian from Shakhtar Donestsk as they confirmed their first arrival of the summer transfer window.
The transfer fee for the 25-year-old is believed to be in the region of around £52m, and Fred will link up with his new team-mates later this summer as he bids to try and help Manchester United challenge for the Premier League title next season.
Willian himself is no stranger to links to Manchester United, with the Chelsea FC star having been touted as a possible target for the Red Devils in recent transfer windows.
Now, the Chelsea FC winger is backing Fred to be a big hit at Old Trafford after the transfer of the midfielder was confirmed this week.
Willian is quoted as saying by Metro: “Of course, no doubt about that. He has a lot of qualities.
“He can improve (them) a lot. He goes to one of the best teams in the world. I am happy for him. I hope he does well at Manchester United.”
Manchester United are likely to be on the lookout for a number of new signings this summer as they bid to try and build a squad capable of challenging Manchester City’s dominance at the top of the Premier League table next season.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news