The tumbler then struck Siobhan Brett on the head as she stood nearby chatting with friends and resulted in her suffering from “a small cut” to her head.
Porteous was later traced and arrested and he appeared at Edinburgh Sheriff Court yesterday (FRI) where he pleaded guilty to a reduced charge of culpable and reckless conduct.
Prosecutor Zoe Nugent told the court the 23-year-old Easter Road defender was standing outside Woodburn Miners Club at around 2am on February 20 this year.
Ms Nugent said: “There were other people outside [the club] and there was an argument involving a group with Mr Porteous.
“He then threw a plastic tumbler into the air in the direction of the group which struck the complainer on the head.
“She suffered a small cut to the head.”
The brief said his client had been involved in an earlier incident that evening where a man had been ejected from the miners’ club.
Mr Harrower said: “He had been out with five close friends and had went to the locus because it is close to his house and he knows the staff there.
“Earlier in the night he had been approached by a disgruntled fan who was then ejected.
“But at the end of the night he was outside the club with his friends and there was a brief exchange.
“Mr Porteous had with him a plastic tumbler and it was empty at this stage.
“Mr Porteous walked away from this but in frustration he threw the tumbler behind him and unfortunately it struck Ms Brett who was standing nearby.”
The lawyer added Porteous “wasn’t looking that way” when he threw the tumbler and he had “momentarily lost control” and “now regrets it”.
The court heard Porteous left the scene “unaware” he had injured someone but after later finding out about Ms Brett he had “apologised” and contacted police.
Mr Harrower added the player is held “in high regard” by his employers and had been fined two weeks wages by the club as a result.
Sheriff Edward Gilroy said: “I accept this was an unfortunate incident and was out of character for you.”
Porteous, from Dalkeith, Midlothian, was fined a total of £320 and told he must pay Ms Brett £200 in compensation.
Porteous pleaded guilty to culpably and recklessly throwing a plastic tumbler which struck Siobhan Brett striking her on the head to her injury at Woodburn Miners Club, Dalkeith, on February 20 this year.
The highly regarded 6ft 2” centre-half has played 99 times for Hibernian since his debut in 2016 and has scored eight goals.
He has also starred for the Scotland U19, U20 and U21 teams and has been called up to the national team’s senior squad four times but is still to be fully capped.