The Belgium international is facing an uncertain future at the north London side after the centre-half failed to agree a new contract with Tottenham Hotspur.
Spurs are rumoured to have offered Alderweireld a deal worth £130,000 a week during the 2017-18 season but the Manchester United target wants £180,000 a week.
Alderweireld’s current deal will expire at the end of next season but Spurs do have the option to extend the Belgium international’s contract by an extra 12 months.
However, if Spurs do opt to activate the clause in Alderweirld’s contract then the 29-year-old would be available for a cut-price £25m deal in the 2019 summer transfer window.
Manchester United are believed to be in the market to sign a centre-half following Mourinho’s frustrations with the inconsistency of Phil Jones, Eric Bailly, Chris Smalling and Victor Lindelof.
Alderweireld admitted that his future at the north London side is far from certain in the current transfer window.
“I have another two years contract, so Tottenham decide about my future,” Alderweireld told Belgian media outlet de Zontag.
“Of course I have my own idea, but that is not the case now.
“The past season was tough, but I’m glad that I could play the last four matches.
“That means that I am ready for the World Cup.”
Manchester United finished in second place in the Premier League table last season to secure a Champions League spot.
The Red Devils lost 1-0 to Chelsea FC in the FA Cup final last month.
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