Towards the end of the Premier League transfer window, the Belgium international appeared destined to be heading for Old Trafford.
Jose Mourinho was, however, to be left frustrated in his efforts to get a new centre-back through the door at Old Trafford, with Alderweireld one of several targets to slip his net.
The former Spurs midfielder told Express Sport of a man who will see a £25 million ($32m) release clause in his contract activated next summer: “I worry about that situation.
“I think if anybody is going to be gone in terms of the window still being open in Europe, he would be the one that possibly does go.
“I’ve always hoped he would be the one that stayed but I get Toby’s situation.
“He’s coming to the end of his career, he wants that big contract, he deserves that big contract and he’s going to get that big contract.
“And if Tottenham aren’t the club to do it, he’ll wait and get it elsewhere.”
Alderweireld has made 115 appearances for Tottenham across three seasons.
The subject of his future has, however, dragged on for some time, with Spurs unable to put fresh terms in place.
Mauricio Pochettino has always maintained that those struggles will not impact on his selection choices, but Alderweireld was left on the bench for a Premier League season opener against Newcastle on Saturday.