But Ferguson denied a deal, reported to be ?26million ($40.3m), had been agreed for the 19-year-old Sao Paulo winger, who is a member of Brazil's Olympics squad.
"It's not correct. We haven't reached an agreement for the player," Ferguson was quoted on Man United's website as telling a press conference in Shanghai on Monday.
"We've shown an interest but until such time as we get a deal agreed we can't say he's our player."
United have already boosted their squad this summer with 23-year-old Japan international midfielder Shinji Kagawa and teenager Nick Powell.
And Ferguson confirmed that the club are hoping to bring in more than one player before the start of the season.
"We've signed two players in the summer: Kagawa and Powell," he said. "We think they both have fantastic potential.
"At this moment we're looking at other options in terms of bringing other players in. We're not lying on our backsides doing nothing. We're trying hard to bring other players to the club."