Leipzig, who host Hertha Berlin on Wednesday, are third in the league on 54 points, seven behind leaders Bayern Munich and three off second-placed Borussia Dortmund with seven games left in the campaign.
The Bundesliga had to break for more than two months due to the Covid-19 pandemic and resumed 10 days ago.
The 25-year-old forward was on target in their 5-0 demolition of Mainz on Sunday and set up two more goals but was diagnosed with a ligament injury a day later.
“Our forward Yussuf Poulsen sustained a ligament injury in his right ankle during the game against Mainz 05,” the club said.
“He will be sidelined until further notice. That was the result of a scan on Monday.”
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies