United signed Harry Maguire, Aaron Wan-Bissaka and Daniel James this summer, but they were linked with many more players.
Costa was injured for an extended part of last season during their league-winning campaign, but United still wanted to get the former Bayern Munich star to Manchester.
But Costa’s agent Giovanni Branchini says manager Maurizio Sarri and previous boss Max Allegri had no interest in letting the winger leave.
“I sincerely say that Allegri and Sarri have never thought of letting him go,” he told the Daily Mail.
“The interest of Manchester United was strong, a club that has always been interested in the Brazilian.
“It was not the only club but in England it was certainly the most active team on the trail of Douglas Costa.
“Douglas has had countless health problems. Last season he was very often injured.
“He is wanting to recover with great professionalism after standing still.
“Juventus never intended to sell him despite the big pressure from United.”
Branchini also stated that Costa would be able to adapt to the Premier League, should he decide to make a future move.
“Douglas is a ‘cool’ professional in the best sense of the word. He is able to adapt to everything,” he added.
“Just think of how well he did in Ukraine, in a country totally different from Brazil.
“He loves Juventus but is able to adapt to every reality. Premier League is a beautiful championship but for now United have failed in all their attempts to convince Juventus to sell him. The player remained in Turin and is a champion.”