FIFA.com reported that the Belgian defender suffered a potential ligament sprain in his ankle only a few minutes after coming on as a substitute.
Spurs boss Andre Villas-Boas knows that being without his best defender will cause the team problems once the season gets underway, but remains hopeful that he will recover in time for the opening game against Crystal Palace on August 18 (also per FIFA):
"He might have sprained ligaments in his ankle so we obviously need the MRI to know the full extent of the injury. He has some range of movement, which gives us some indication that probably it may not be too long. [It] Depends on the extent (of the injury) from the MRI. I think because of the range of the movement that he has I think we have the possibility he will be back for the start of the season."
Tottenham are currently in Hong Kong on their preseason tour, taking part in the Barclays Asia Trophy, so it is not yet clear whether Vertonghen will need to return to England for his scan or whether he'll remain with the team for initial observation and treatment.
Depending on the severity of the sprain, the ankle injury could keep Vertonghen out for up to five weeks according to physioroom.com.
Despite William Gallas leaving Tottenham on a free transfer this summer, the first-team is still well-stocked in central defence.
Even being potentially without Vertonghen, Villas-Boas will still be able to call upon Steven Caulker and Michael Dawson. Younes Kaboul is also still a Spurs defender, despite being sidelined by injury for most of last term.
Even so, Vertonghen was one of the top defensive performers in the Premier League last season and his versatility, as well as his all-round quality, were a big plus-point for his team.
Vertonghen performed at both left- and centre-back during the season, and his ability to break forward into midfield at pace with the ball was often a tactic used to push play farther up the pitch.
The 26-year-old scored four times in the Premier League and provided three more assists; not a bad return at all for a defender, while he also ranked in the top-20 for clearances and tackles made per game last season.
Aside from his technical qualities, Vertonghen quickly showed himself to be a leader of the back line and his presence would be greatly missed if his absence proves to be an extended one.
The defeat at the hands of Sunderland means that Spurs will play a third-place playoff match against South China on Saturday, while Sunderland will play Manchester City in the final a day later.
Spurs were already without the injured Gareth Bale and now Vertonghen's absence will make their preparations for the new season all the more difficult.