With Spurs trailing 1-0 after an early goal from Donny van de Beek, Vertonghen and Alderweireld came together in the air in a sickening clash which left both players sprawled on the turf in the Ajax penalty area.
Vertonghen needed lengthy treatment on a nose injury - with blood spilling from a gaping wound on the ridge of his nose - and left the pitch before replacing his blood-stained shorts in order to continue.
There was another brief delay as referee Mateu Lahoz appeared to be checking whether Vertonghen was fit to play on, and the Belgian briefly re-entered the field of play before deciding he could no longer continue.
There was immediate concern for Vertonghen as he shook his head before deciding to come off with apparent concussion, with the defender looking groggy and unsteady on his feet as he had to be helped down the tunnel.
Vertonghen tried to return to the field of play but quickly indicated he needed to be replaced with Sissoko coming on in his place.
However, Vertonghen passed all relevant concussion tests on Tuesday night, and will be assessed further on Wednesday in a boost for Spurs.
#thfc Vertonghen has passed all concussion tests this evening. More tests tomorrow but, for now, looking positive.
— Dan Kilpatrick (@Dan_KP)
When asked about Vertonghen's injury after the game, Pochettino told BT Sport: "I didn't see him. Of course, we will assess him in the next few days."
Back in 2013, a spokeperson from Headway - a charity which helps to improve life after brain injury - described Tottenham's behaviour as "irresponsible" when they allowed Hugo Lloris to play on in a match against Everton after the goalkeeper lost consciousness following a collision with Romelu Lukaku.