United boss Jose Mourinho tried to sign England international Dier before eventually splashing out £40m on Chelsea's Nemanja Matic instead.
Dier was keen on a move to Old Trafford but Spurs supremo Daniel Levy bluntly denied to do business with the Red Devils.
That potential transfer collapsed but it appears that Tottenham still have a fight on their hands to keep hold of Dier.
The Sun claim German giants Bayern are ready to test the north Londoners' resolve by offering £50m for the versatile midfielder.
It is said that Carlo Ancelotti is a big fan of the 23-year-old and is planning to make the mega-money bid in the coming weeks.
Bayern believe they will be able to convince Spurs and Levy into selling unlike United.
Tottenham are yet to complete a deal for their own this summer and funds are tight for Mauricio Pochettino.
But the potential sale of Dier - added to Kyle Walker's £50m move to Manchester City - would help Pochettino's pursuit of his targets.
Dier has become a key figure under Pochettino and has played 100 games for the club in all competitions over the past two seasons.
He joined Spurs from Sporting Lisbon in August 2014 for £4m and Pochettino will not want to let him go.
But making such a huge profit on him could prove too hard to resist for Levy and co.