The two Belgians both went for the same header with Vertonghen heading his team-mate instead of the ball.
The 32-year-old received lengthy treatment on the pitch and on the sidelines before changing his shirt.
Vertonghen returned to the pitch for Spurs but just moments later he signalled he could no longer continue and appeared to nearly collapse on the sidelines in distressing scenes.
Moussa Sissoko was the man to replace the former Ajax defender as Mauricio Pochettino reorganised his side.
Ajax started the better of the two sides taking an early lead through Donny van de Beek.
Tottenham seemed to kick into action after falling behind, but the sickening collision which saw the end of Vertonghen’s game left them reeling again.
BT Sport presenter Gary Lineker expressed his concern for Vertonghen.
He explained: “Jan Vertonghen, a bit concerning how he reacted when he went back on the field of play and then came off.
“He seemed fine there and then he kind of lost his legs and everything. Whether he kind of feinted.
“He’s okay in the dressing room apparently.”
And Tottenham legend Glenn Hoddle echoed the concern of Linker.
“Look now, it’s horrible to see. He’s absolutely feinted, he’s gone, his right leg,” he said.
Vertonghen was left spitting blood but was determined to carry on in the first leg of Spurs’ Champions League semi-final.
Fans expressed their concern over Vertonghen being allowed to return to the field at all.
One tweeted: “Genuinely hope Vertonghen is ok. That looked a really nasty head injury. Cannot believe the medical team allowed him back on! You could see clearly that he was all over the place. Shocking.”
Another said: “I say it alot but theres so much football can learn from rugby. Vertonghen should have been taken for a HIA (head injury assessment) with a replacement brought on for the duration. If passed fit, he comes back on, if not, the sub is permanent.”
At the beginning of the second half BT Sport commentator Darren Fletcher gave an update on Vertonghen.
The Belgian was receiving treatment in the medical room at the Tottenham Hotspur Stadium.
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