According to The Mirror, Mauricio Pochettino has told club chairman Daniel Levy to defy any advances from the Europa League champions who have been readying up a £50m ($64m) bid and are also prepared to double Dier's current wages of £70,000 ($90,272) per week.
United officials believe Dier wants to leave Spurs and join the Red Devils with the England international currently being Jose Mourinho's number-one midfield target after a move for Nemanja Matic stalled.
However, the 23-year-old is someone Pochettino intends on keeping, having rejected an offer from United for his services following the end of the 2016/17 season.
Having signed a five-year-contract in September 2016, Dier could now be awarded with a new deal with Spurs well aware that he could earn double his current salary with a move to Manchester.
The same Mirror report also claims Tottenham feel that given their recent performances in the league as well as boasting Champions League football, they are no longer vulnerable to potential raids for their stars, having sold the likes of Michael Carrick and Dimitar Berbatov to United in the past.
Dier joined Spurs from Sporting Lisbon in 2014 and has proven to be a valuable player for the north London side thanks in part to his versatility, being able to operate in his preferred position as a defensive midfielder, centre-back or right-back.
However, the Cheltenham native lost his place in midfield to summer signing Victor Wanyama last season and could be offered first team action in that role at Old Trafford.