James Maddison was stretchered off during Spurs' 1-1 draw against Newcastle in pre-season and Thomas Frank has issued an update.
Spurs took the lead in South Korea through Brennan Johnson but the Magpies equalised before half-time with Harvey Barnes getting on the scoresheet.
The fixture was significant as it could be the final appearance for Son Heung-min who announced he would be leaving the club this summer amid interest from Major League Soccer.
In the second-half, Maddison hobbled off the pitch before collapsing in a heap as medics rushed to his aid. He was stretchered off the field as his teammates looked on in horror.
Speaking after the game, Frank claimed the injury was 'bad' and suspects it was on the same knee that kept Maddison out of action at the end of last season.
"We're pretty sure it was the same knee he injured before," Frank said.
"I think sometimes in life and football things can be both beautiful and brutal. That's what we got today. It looks like with Madders a bad injury and then on the other side unbelievable scenes for Son from his team-mates and the respect from the Newcastle players.
"First we had the walkaround and then the team-mates gathered around and he was emotional. In the changing room it was more of the same.
"I just said a few things but not much because it's about Sonny and then he said a few things. It was beautiful."
Maddison was ruled out of the remainder of the Premier League season during Spurs' Europa League first leg win over Bodo/Glimt at the start of May with a knee problem.
Spurs kick off the new season in just ten days in the UEFA Super Cup against Paris Saint-Germain and Frank is now left with the prospect of being without a natural no.10 with Dejan Kulusevski also sidelined.
Son is also likely to have left the club before that fixture after announcing his departure on Saturday.
He said: "Before we start the press conference, I wanted to say I have decided to leave the Club this summer. Respectfully the club is helping me with this decision.
"It was the most difficult decision I have made in my career. Such amazing memories. It was so hard to make the decision.
"I need a new environment to push myself. I need a little bit of change - 10 years is a long time. I came to north London as a kid, 23 years old, such a young age. I leave this club as a grown man, a very proud man.
"I want to say thank you to all the Spurs fans for giving me so much love. I hope the goodbye is also good timing and this is the right time to make that decision. I hope everyone can accept that and respect that."