Joshua Rae, who is just 13 and 6ft 2in, came on for the final six minutes of Hamilton Academical's Under-20s 3-1 victory away to Partick Thistle.
And the teenager from Croy in North Lanarkshire, who was once offered a contract with Atletico Madrid, is now expected to seal a move that would mean he joins England international goalkeeper Fraser Forster at Celtic.
Joshua, a Celtic fan whose early hero was Hoops keeper Artur Boruc, first came to public knowledge as a 12-year-old. He impressed an Atletico Madrid scout while scoring twice as a goalkeeper in a match when he was on holiday in Spain last year.
He was in Benidorm, playing in an Under-14s tournament with a team from Jordan he had been approached to join, while having a kick-around in a local park. After the match an Atletico Madrid scout, who Mr Rae thought was a parent of one of the Madrid team, asked if Joshua was interested in going to the Spanish capital for a trial.