The 49ers activated linebacker Kwon Alexander off injured reserve Friday to make him eligible to play Saturday in the divisional round of the NFC playoffs against the Minnesota Vikings.

The 49ers placed defensive lineman Kentavius Street on injured reserve to make room on the active roster for Alexander.

Alexander returns to action a week earlier than the 49ers originally thought was possible. He will play Saturday against the Vikings at Levi's Stadium. It is not known exactly how the 49ers plan to use him, but Dre Greenlaw still is expected to play a vital role.

“I know Kwon will fly around,” 49ers coach Kyle Shanahan told NBC Sports Bay Area. “He’ll hit. He’ll be energetic. He’ll get everyone going. I think everyone will feel his energy on the field. And we’ll see how it goes.

“We’re not going to throw him out there, just down-in and down-out. But we don’t have a plan, where it’s only going to be ‘this’ amount."

[RELATEDHow much will Kwon play in his return?]

Alexander has not played since sustaining a torn pectoral on Oct. 31 while tackling Arizona Cardinals running back Kenyan Drake. Alexander underwent surgery the following week.

Each team is allowed to bring two players per season off injured reserve. Earlier this season, the 49ers activated defensive lineman Kentavius Street off IR.