Tottenham are said to be pessimistic over Toby Alderweireld's future.
United are able to activate a clause in his contract reportedly just £26 million.
The Red Devils are long term suitors of Alderweireld and Tottenham can have no say over where he goes.
Their only chance is to agree the Belgian to an extension, but at this point, Alderweireld is so close to an exit that it is more unlikely than ever.
The centre-back is one of Tottenham's mid-ranking earners, and even if he took a similar place in Manchester United's wage structure, he would still likely earn more than Spurs' highest paid player.
United and Tottenham are separated by just three points in the Premier League table.
For Tottenham it would be a blow to lose Alderweireld, highlighted by the fact they have struggled without him.
Their decision to rest him last weekend backfired badly as they lost to Southampton.
Spurs fans are unhappy with the developments...
Such a small club mentality. Selling to direct rivals.— Jay Bear (@JayLangg) March 14, 2019
and so it begins.......The heirachy at Spurs showing ZERO ambition and happy to see the dismantling of this squad. Be interesting to see if they increase ST prices next Monday. If they do then im done with football.— The Gravy Train (@graves7328) March 14, 2019
shocking - should do everything they can to keep him and def not sell to a rival— MB Trading (@MBdaytrading) March 14, 2019
Toby has shown great passion this season, is playing regularly, hopefully we can put a deal together for for him, such a key player #THFC— James Bradley (@JamesBradley88) March 14, 2019
Hope this is just another unfounded rumor. Toby's been great.— More Sea Power (@DivertimentoNo1) March 14, 2019
Selling top players to direct rivals really sticks in the throat. They won’t be rivals for long if we keep doing it— Anthony Pepera ✏️ (@otheranthony) March 14, 2019