Mauricio Pochettino fears striker Harry Kane may have damaged ankle ligaments in Tottenham's 1-0 victory over Sunderland.
Kane scored the winner, his second goal of the season, at White Hart Lane but had to be carried off on a stretcher following a collision with defender Papy Djilobodji.
The 23-year-old was later seen leaving the stadium on crutches and wearing a protective boot on his right foot.
"We will assess him tomorrow. It was tough, he twisted the ankle," Pochettino said.
"Now he feels pain and we see tomorrow. It's painful and we need to wait.
"I'm sure there may be a problem with his ligaments but it's difficult to assess today. We need to wait."
Kane would most likely have been rested anyway for the League Cup match against Gillingham on Wednesday but Spurs travel to CSKA Moscow in the Champions League next week, between Premier League games against Middlesbrough and Manchester City.
A longer lay-off could also mean the forward misses England's World Cup qualifying fixtures against Malta on October 8 and Slovenia three days later.
Eric Dier and Mousa Dembele limped off in the second half against Sunderland as well but Pochettino said both were suffering from cramp, rather than anything more serious.
Kane, Dier and Dembele all faced Monaco in the Champions League on Wednesday - although Dembele only came on for the second half - and the trio were involved at Euro 2016 with England and Belgium respectively
"Dier and Dembele only feel cramps in the hamstring, it's not that big an issue," Pochettino said.
"When you're in different competitions, Champions League is a different competition, we spent a lot of energy on Wednesday, it's different to the Europa League. It's new for us so it's important to learn.
"All of them are internationals, they come after a difficult summer, after playing in the Euros. It's difficult with holidays and pre-season and it's difficult to get fit."
Tottenham's victory over the struggling Black Cats means they climb to third in the Premier League table and maintain their unbeaten start to the season.
They managed 31 attempts on goal and had been the dominant force, even before Adnan Januzaj was sent off for a second yellow card late on.
Pochettino had been critical of his side's energy levels in their defeat to Monaco last week but the Argentinian was satisfied, even if it took a hashed clearance from Papy Djilobodji for Kane to break the deadlock.
"It was a good result," Pochettino said. "For the chances we create it's difficult to understand why only 1-0.
"We created many chances but okay, I'm happy with the performance and attitude and the way we played from the first minute. That's the way we need to play every game, not only some games."
Pochettino hauled off Son Heung-min at half-time last week but the South Korean was arguably Tottenham's best player against David Moyes' side.
The winger opted to play at the Olympics this summer rather than undergo a full pre-season with Spurs, and was almost sold in the transfer window, just one year after joining the club.
"For him last season was tough for him. He came to see me and said 'I need your help'," Pochettino said.
"I said, 'okay, always my door is open' and we decide to stay. He is a quiet person, nice person and then you need to fight for your place.
"But it's true from the beginning after the Olympic Games his idea was to leave to go to Germany. One thing is what the player wants, the other is the club decision.
"In his mind, he would like to move, but in the end he accepted to stay and fight for his position."
Sunderland sit 19th in table and are still without a win in the league under Moyes.
The Scot also responded to suggestions that full-back Patrick van Aanholt was left annoyed, after being told in the warm-up he had been replaced in the starting line-up by Jason Denayer.
"For medical reasons we chose to withdraw him, I won't follow up if you don't mind," Moyes said.
"I'd like to be straight. We advised the referee very late on. I got word of something very late. People can get injured in the warm-up."
On his side's poor start to the campaign, Moyes added: "We need momentum, to pick up and find a way of getting some wins. We need to feel better about ourselves."
Source: PA
