United boss Jose Mourinho is looking to bolster his midfield ahead of the addition of Champions League football next season.
Nemanja Matic is an alternative to Dier but Chelsea are not keen on selling to a direct rival, especially after United beat them to the signing of Romelu Lukaku earlier this week.
Tottenham do not have the best relationship with the Red Devils when it comes to transfers after selling them Dimitar Berbatov in 2008.
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Eric Dier would cost Manchester United over £50million
Manchester United definitely after Eric Dier from Spurs
Kaveh Solhekol on Man Utd target Eric Dier
But Solhekol believes a bid northwards of £50m will make Spurs consider letting Dier go.
"United still as well definitely after Eric Dier from Spurs," Solhekol said on Sky Sports.
"He's one of their two main midfield targets.
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Eric Dier has told his friends he wants to leave Tottenham for Man Utd
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"Dier has four years left on his contract and it's notoriously difficult to buy players from Tottenham.
"They don't want to sell and it's thought only an offer over £50million would make them think again.
"Another Manchester United midfield target is Nemanja Matic but Chelsea are reluctant to do business with United after what happened with Lukaku."
Dier has made 101 Premier League appearances for Tottenham since joining from Portuguese side Sporting Lisbon in 2014.