Work to repair what has been described as "extensive damage" at Taynuilt has been scheduled to be completed by Monday.
ScotRail said a bus shuttle service will operate from Oban to Dalmally, calling at stations along the route.
The operator said the bus replacement service would run "as close to train time as possible".
No rail services will operate on the Glasgow to Oban line over the weekend, after a lorry collided with a bridge.