Souness Clark grabbed the woman’s breast as he travelled on an easyJet flight from Edinburgh to Berlin in January last year.
Clark, from Clydebank, was among 200 supporters on the plane travelling to Germany to watch the Ibrox club play a challenge match against RB Leipzig.
Flight attendants struggled to keep order during the flight as the rowdy footie fans began shouting and singing club songs.
And as one female air steward, who cannot be named due to legal reasons, attempted to serve beer to a passenger Clark reached out and grabbed and squeezed her breast.
The easyJet employee was said to have been left “physically shaken” by the sexual attack.
The “out of control” easyJet flight was then met by German police officers when the plane touched down in Berlin’s Tegel Airport.
Clark, 28, pleaded guilty to sexually assaulting an air steward on a flight between Edinburgh and Berlin on January 14 last year when he appeared at the Capital’s sheriff court on Monday.
The disgraced Rangers supporter also had not guilty pleas accepted to assaulting a second female steward by seizing her on the body and to behaving in a disorderly manner by shouting and singing.
He was also alleged to have acted in an aggressive and intimidating manner while also striking the overhead lockers and refusing to comply with cabin crew instructions.
Fiscal depute Mark Keane told the court there were “a large number of passengers” on board when a number of fans became rowdy.
Mr Keane said: “[Due to this] The cabin crew were not in a position to bring the drinks trolley to the front gallery.
“One of the stewardesses on the flight had a tray of beer for a passenger and as she passed the accused he reached out and grabbed her by the breast and compressed it.
“She hit his hand away and continued on towards the front gallery. She was physically shaken by the incident.
“She told another member of staff what had happened and as the aircraft landed she was made aware the flight was being met by German police.”
The fiscal added Clark was taken from the flight by police officers to a local hospital and was subsequently cautioned and charged for the offence.
Defending solicitor Michael Gallan said his client had acted out of “drunkenness” and that he had “no real recollection” of the sex assault on the air steward.
Mr Gallan asked Sheriff Michael O’Grady QC not to decide whether Clark should be on the sex offenders register until he could give his full mitigation at the sentencing hearing.
Sheriff O’Grady agreed to the request and deferred full sentence on Clark to later this month.
A source said: “The flight was really horrific. There was shouting, singing and swearing coming from the supporters and most of them were really drunk.
“Some of the language and the words of the songs were disgusting. To be honest, I was shocked some of them were allowed on board they were that far gone.
“The fans were really out of control at some points and I was not surprised cabin crew had to phone the police to meet the plane when we landed in Germany.
“I didn’t see the incident with the stewardess but you could see from other members of the cabin crew something bad had happened.”
Around 8000 Rangers supporters travelled to watch their team play the friendly match against RB Leipzig at the Red Bull Arena on January 15, 2017.
Rangers lost the match 4-0 with £13 million Scotland striker Oliver Burke among the scorers for the crack German outfit.
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