The Belgium global has not agreed a new deal with the club, with a clause in his contract stating he can leave for £25 million before the last two weeks of next year's summer transfer window if they activate a contract extension.
Barca now have six centre-backs in their squad and only three - Gerard Pique, Samuel Umtiti and new signing Clement Lenglet - appear guaranteed to be at the club when the season begins.
Over weeks, a deal with Tottenham for Alderweireld had stalled and that's where many other names came to the fore. Spurs felt this will be the right move to cash in on the former Atletico Madrid man at an optimum price.
Manchester United finished in second place in the Premier League table last season to secure their best finish since Sir Alex Ferguson's retirement.
A number of clubs around the world have been attempting to land Mina, with Everton and Manchester United seemingly at the front of the queue - but both teams may just be backing off.
Alderweireld to United? Watch this space.
United monitored his situation closely and was always the top most priority.
The Belgium World Cup defender remains available for transfer before next Thursday's 5pm transfer deadline. Although he will have to fight for a place given United's resources in central defence.