On Wednesday morning, a fire at the Myrbacken station damaged electric cables, causing all trains heading north of Stockholm to grind to a halt.
The Arlanda Express train, plus commuter trains heading to Uppsala and beyond, were all replaced with buses.
Authorities said at the time that the trains should be on the move again by the end of the day, but revised the estimate on Friday morning, stating that delays may continue until Monday.
"It may even be longer," Beisi Sundin at the Swedish Transport Administration (Trafikverket) told the TT news agency.
"We need to do a comprehensive electric analysis which is complicated and time consuming."
While the Arlanda Express line has since been fixed, commuter trains can only reach Märsta, meaning passengers heading further north must take buses, or get redirected.