Tottenham boss Mauricio Pochettino said he is concerned by Dele Alli's injury after seeing the player substituted clutching his left hamstring in the victory against Fulham at Craven Cottage.
Spurs, who won 2-1 thanks to a stoppage-time header from Harry Winks, are already without Harry Kane for two months after scans confirmed ankle ligament damage.
Son Heung-Min is in Asian Cup action this month leaving Spurs short of numbers ahead of a midweek Carabao Cup semifinal second leg against Chelsea.
"We need to assess [Alli] in the next few days," Pochettino said. "It doesn't look great."
"On the pitch, I think we all agree that when you see him put his hand on his hamstring it's a situation where it's not great to see that.
"It's not a worry, it's a massive opportunity for different players to play. Like I told you with Harry Kane and now with Dele Alli, we hope it's not a big issue but the most important thing is to believe. We go there [to Chelsea] trying to win the game and go to the final.
"Lucas Moura was training today at the training ground. He's going to be okay. Today we didn't want to take a risk with him but he's nearly 100 percent to try to help the team.
"Maybe it's not going to be Dele Alli [at Chelsea], but we're going to have Lucas Moura on the bench or maybe starting from the beginning. We'll see how we're going manage him now."
Pochettino was delighted with Winks' late winner, having urged the midfielder to chip in more regularly.
"That thing today, we were talking in the last few weeks that it's something he needs to improve -- arriving in the opponent's box and trying to score more goals," said Pochettino. "That's his second goal in the Premier League.
"With his quality, how he plays, in possession he needs to add and improve those two different areas in his game without the ball, be more aggressive -- he's doing that and I'm so happy -- and of course trying to score more goals, because always for a midfielder if you add goals, like [Ivan] Rakitic and [Luka] Modric, you start to think that you're a top, top player.
"Today was fantastic. I advise all people to watch the action and how it started. He recovered the ball in a very deep position, like a full-back, and then how he ran with great determination to score, it was a fantastic example for the players."
Winks' goal was set up by out-of-favour winger Georges-Kevin Nkoudou, who made only his second appearance of the campaign when he replaced Alli in the 86th minute.
"At the moment, like other players, we struggle with players we have injured and of course he has the possibility to play," said Pochettino.
"Of course he's disappointed because he didn't play too much until now, but now if there's the possibility like today and he shows this type of performance -- I think the cross was perfect -- of course he will have the possibility to play."