The Daily Star reports that United could make a move for the 22-year-old France defender in the January transfer window.
Hernandez signed a new long-term contract with Atletico in June, which will keep him at the club until 2024.
The highly-rated defender has a £72million release clause in his contract.
“Atletico Madrid are the club of my life,” he said after signing his new deal in June.
“They’ve given me everything and I’m very happy with my renewal because it was what I wanted most.
“They’ve always trusted me, since I came into the youth team and gambled on me, I’m very grateful.
“For me it’s an honour to have been part of our academy and have made it to the first team, with the club gambling on me like that.
“I can’t do anything else than thank them for their trust and pay them back on the pitch.”