The Red Devils are chasing another central midfielder to take the goalscoring and creative burden off Paul Pogba.
With double figures in goals and assists for Sporting in the Portuguese league last season, Fernandes is an ideal fit.
But the Daily Mirror indicates that United want Fernandes on the cheap. Sources in Portugal also back up the claim.
United have made a €35 million (£31m) bid for the player and do not want to go too much higher.
However, Sporting want around €25 to €35 million more.
Other teams are interested, including Tottenham, but United feel they have a clear run at Fernandes and will bide their time to get him for the right price.