The 22-year-old was forced off the pitch in Celtic's 3-0 win over Alashkert FC after netting twice against the Armenian side.
Dembele could miss his side's next three fixtures in the Champions League, leaving manager Brendan Rodgers short of attacking options in the meantime.
"Moussa will be out for a few weeks. Thankfully it's not a longer-term hamstring. Sometimes these things can be six to eight weeks but it's not that - it's two to three weeks maximum," Rodgers told the club's website.
"It was unfortunate for him as he's looked very fit in pre-season.
"We had a scare with Odsonne as well and he only just rejoined training on Monday. After the game, his knee had swollen up. He hadn't trained for a few days but he looked fine on Monday in training."
Celtic will commence their Scottish Premiership campaign against Hamilton Academical on August 4.