Herrera’s contract is due to expire at the end of the season and ESPN FC report that he is considering an offer from Paris Saint-Germain.
Niguez has been followed by United scouts ever since his standout season on loan at Rayo Vallecano in the 2013/14 season.
The 24-year-old is seen as a good fit for Ole Gunnar Solskjaer’s midfield, where he could work well alongside Nemanja Matic and Paul Pogba.
However, Atletico Madrid are understood to require that Niguez’s €150 million (around £128 million) release clause is met if a sale goes ahead.
The clause was inserted into a deal signed by the Spain international in 2017, which ties him to the capital club until 2026.
Niguez, who can operate across midfield, has scored six goals in 38 games in all competitions for Diego Simeone’s side this season.
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