West Brom lose Olsson for six weeks
Albion boss Roberto Di Matteo confirmed the club's vice-captain could be sidelined until mid December.
It is a big setback for the Baggies as Olsson has been a key figure in their fine start to the campaign in the Barclays Premier League.
Di Matteo admitted: "With Jonas, we're looking at a longer injury - rather than a few weeks.
"I would like to keep it down to weeks, but it won't be two weeks. It will definitely be around the five or six-week mark.
"It's an injury that can improve dramatically but he's not going to be back within two weeks, that's for sure."