Alli went down clutching the back of his left leg late in the 2-1 win over Fulham at Craven Cottage on Sunday.
And Poch now faces Thursday's Carabao Cup semi-final second leg against Chelsea without his England international, as well as the injured Harry Kane.
Spurs chief told Sky Sports: "I think we all see that during the action there was an injury in his left hamstring but now we need to assess him in the next few days.
"I hope it is not a very big issue but you know very well that when this type of injury appears we need to be careful. First of all we need to assess what is going on in his muscle."
Pochettino takes his team to Stamford Bridge this week with a 1-0 aggregate lead from the League Cup first leg.
And the Argentine coach already knows he will be without captain Kane until at least March after damaging ankle ligaments.
With Son Heung-min on international duty at the Asia Cup, Poch will have his fingers crossed over Alli's fitness.
Keeper Hugo Lloris said: "We don't want to see our players leaving the field in this way but hopefully it's not too bad.
"It's a period that's very difficult, a few important players are injured but it gives the opportunity to some other players to show their quality."
Georges-Kevin N'Koudou, Alli's replacement, took his chance by teeing up Harry Winks for a dramatic late winner at the Cottage.
Poch praised the duo, saying: "It was fantastic for G-K N'Koudou, his first game of the season in Premier League.
"The action was brilliant. After 93 minutes Harry Winks recovered the ball in a deeper position and he believed and arrived to the box.
"The cross was fantastic from N'Koudou and he arrived with the determination to score."
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