The 28-year-old was forced off during Sunday's 2-0 Premier League win over Newcastle United following a clash with Lewis Miley. Assessments have since ruled him out until at least April.
Tielemans joins Boubacar Kamara and John McGinn on the sidelines, leaving Emery short of first-choice midfielders. Kamara is out for the season after knee surgery, while McGinn is expected to miss six to eight weeks following an operation earlier this week.
"We know about Kamara, McGinn and Tielemans," Emery said. "Kamara is not going to play this season. McGinn is six to eight weeks out, and Tielemans is eight to 10 weeks out. We need to manage our midfielders carefully in the matches ahead."
There is some relief on the horizon. Ross Barkley is close to returning after training individually, while Amadou Onana is nearing full fitness. Villa are also close to bringing back Douglas Luiz, with the Brazilian set to return after his loan at Nottingham Forest is cut short.
"I think Luiz is close to happening," Emery added.
Villa host Red Bull Salzburg at Villa Park on Thursday in their final Europa League league-phase match. They have already secured qualification for the knockout rounds and will aim to finish top of the group despite their injury concerns.
Leon Bailey and Tammy Abraham will not feature in Europe, while Emery confirmed there has been no change to the situation of loan midfielder Harvey Elliott as the transfer window nears its close.
Belgium international Youri Tielemans said he "feels incredible" after penning a five-year contract to join Manchester United from fellow Premier League side Aston Villa.
Liverpool manager Andoni Iraola has moved to ease uncertainty surrounding Harvey Elliott, delivering his first public comments on the midfielder's future since taking over at Anfield.
Xabi Alonso says instilling a relentless desire to improve will be the foundation of Chelsea's rebuild as he prepares for his first Premier League campaign in charge at Stamford Bridge.
Manchester United have confirmed the signing of Andrey Santos from Chelsea, while the Red Devils are also closing in on a deal for the transfer of Youri Tielemans from Aston Villa.
