He's affectionately known as 'the brickie' after proving nearly everyone wrong under Ange Postecoglou's guidance.
But Frank McAvennie turned on Celtic star Anthony Ralston as he claimed the right-back looked like he'd walked straight "off a building site" and into St Mirren's SMISA Stadium.
Scotland cap Ralston has had a whirlwind end to 2021, standing up and being counted when the cards were stacked against a ravaged squad in late summer when Postecoglou first took over.
And his headed winner in added time at Ross County will go down as a memorable moment of this season.
But McAvennie wasn't ready to give him an inch of leeway when he brought up the 0-0 draw in Paisley - which now sees Celtic going into the winter break six points behind Rangers at the top.
Speaking to Football Insider, he said: "I was at the St Mirren game and I thought, ‘Dear me he’s gone backwards’.
"Oh my God, he was hopeless. He looked bit-part. Honestly, he was playing like he had just come off a building site.
"He was just crashing around into people. That’s the player I was always convinced wouldn’t make it.
"He looked great earlier this season, that’s why he got the Scotland call-up.
"But he hasn’t looked the same and I was so disappointed with him against St Mirren.
"I was disappointed with everyone if I’m honest but Ralston was really poor."
