Partick Thistle midfielder Gary Fraser has apologised for the "moment of madness" which saw him fire a ball into the Celtic Park crowd.
Fraser reacted with frustration late on during his side's 2-0 defeat to Brendan Rodgers' side on Wednesday night and smashed the ball at a female Celtic supporter.
Thistle chiefs have now released a statement insisting the 23-year-old "intended to hit the wall at the front of the stand" but admits his mistake was "inexcusable."
They have now confirmed Fraser, who was booked by referee Alan Muir following the incident, has now contacted the fan by phone to offer an apology, which has been accepted.
Fraser added: "I can only apologise both to the supporter I struck and everyone else who was at the ground.
"I don't know what I was thinking. It was a moment of madness and stupidity from me.
"Of course it should never have happened but I absolutely did not mean to hit the ball into the stand and certainly had no intention of hitting anyone with it.
"It reflected badly on me and on the team and I feel like I've let down the club. As soon as it happened I realised what I had done and was devastated.
"All I can do is say that I am genuinely sorry and that is why I wanted speak to the supporter myself today."
Thistle have also confirmed the fan and a guest have been invited by Fraser to see the Hoops take on Thistle at the Energy Check Stadium at Firhill when the sides meet next month.
Fraser had started the game on the bench and had only been on the pitch for a matter of minutes after replacing Blair Spittal when the flashpoint occurred.
He was loudly booed by the home support after the incident but Celtic boss Rodgers gave a tempered response.
"I didn't see it and just caught the tail end of it," he said. "I would have to give the benefit of the doubt to the player as I would sincerely hope he wouldn't be smashing the ball into a crowd on purpose.
"You get that close to supporters who are paying money to watch a game then you shouldn't be doing things like that.
"Maybe it was frustration from the young player because he's not playing or he is losing the game but you don't do that."
Thistle manager Alan Archibald -- whose side remain bottom of the table -- backed Fraser, saying: "He didn't mean it. He tried to hit the boards out of frustration.
"He is frustrated he never started the game. I don't think there was any malice, he is not that type of lad.
"We will deal with it. He has not done it deliberately and he apologised at the end.
"I don't think anyone in their right mind would try and do that from so close, especially the way he strikes the ball."
The Scottish Football Association has confirmed no further action can be taken against former Bolton youngster Fraser as the incident was dealt with at the time by the match officials.