Bridgeton Station in the east end opened nearly one hour late as a result, forcing at least ten trains to run through without stopping.
ScotRail said it was caused by “short-notice sickness” by the member of staff who was due to have opened the station.
The doors should have been unlocked in time for the first train at 6:15am, but passengers were not able to get in until around 7am.
Those planning to alight at Bridgeton had to get off at Argyle Street Station in the city centre or Dalmarnock to the east instead.
The single member of staff at the station had also been due to open the ticket office at 6:40am.
ScotRail tweeted: “I am sorry to anyone who experienced any difficulty with their commute this morning due to this.”
ScotRail described the incident as “not common, but not unheard of”.
A spokesperson said: “We’re usually able to arrange cover from another station within the area, but when it’s really short notice, it take time for cover to arrive.
“We arranged cover to open the station when it became apparent there was a short notice absence.”