The Belgium international was forced off the pitch in the first half of the first leg at the Tottenham Hotspur Stadium following a clash of heads with Toby Alderweireld.
Vertonghen, 32, headed the back of his fellow countryman’s head shortly after the half-hour mark while trying to get on the end of a free kick.
The former Ajax man began to pour with blood but was patched up and soon returned to the field.
However, seconds after being deemed fit to return to action by Tottenham‘s medical team, he began suffering from concussion-like symptoms and almost fainted.
The decision from Tottenham doctors to let Vertonghen return to the pitch was widely criticised, with many accusing Spurs’ medical team of negligence.
Tottenham addressed the matter on Wednesday night and revealed Vertonghen was cleared for action after coherently answering several questions from club doctors.
“Jan Vertonghen has undergone further assessment today (Wednesday 1 May) after sustaining a head injury in last night’s Champions League semi-final first leg against Ajax,” a club statement read. “He also suffered a small cut to his nose that was bleeding heavily.
“The Belgium defender was assessed on the pitch yesterday immediately after the incident with our medical team strictly following Football Association concussion guidelines.
“Following testing he was judged to be alert and answered all questions correctly and lucidly, deeming him fit to return to the field of play.
“All available video footage was relayed to our on-pitch medical team and they were able to confirm that he had suffered no loss of consciousness.
“Jan was immediately withdrawn as a result of the player informing medical staff that symptoms were developing suddenly and that he no longer felt stable standing up.
“Tests today have been clear and testing will continue for the next few days. Additionally, as is standard Club policy with certain injuries, we shall also be seeking independent advice and Jan is due to see a neurologist, who specialises in elite athletes, tomorrow.
“The player has reported no ill-effects today.”
Although his medical team were widely criticised for their allowing of Vertonghen to return to the pitch, Tottenham boss Mauricio Pochettino is adamant they followed the proper protocol for head injuries.
“I wasn’t involved. It was the doctor’s decision,” said Pochettino. “The rules and the protocols are there.
“Our medical staff followed the protocol.
“He’s OK. We hope it is not a big issue. He walked away from the stadium.
“We know we have to keep watching and monitoring him because it was a big knock.”
Tottenham suffered a 1-0 home defeat to Ajax courtesy of a first-half strike from Donny Van De Beek, which has put Ajax on course for their first European Cup final since the 1995-96 season.
Pochettino’s side will look to overturn the deficit next Wednesday in the second leg in Amsterdam to reach their first Champions League final.