The Athletics activated Gelof (knee) from the 10-day injured list Monday.
Gelof is ready to roll after missing the past month of action with a right knee laceration. The 26-year-old was in the middle of a nice bounce-back season before getting hurt -- slashing .273/.327/.476 with 11 home runs in 67 games -- and should regain his role as the Athletics' primary third baseman.