The 22-year-old returned to Celtic Park on a permanent deal in the summer after spending last season on loan from Benfica. He was given a spot in the starting lineup in the Glasgow derby, helping his side to a 3-0 win over Rangers.

Following the departure of Matt O’Riley to Brighton for a club record fee believed to be in excess of £25 million, Hartson believes the Portuguese midfielder could follow in his footsteps.

“Brendan likes signing players that he feels he can improve,” he said. “Brendan’s brilliant on the training ground and he likes to work with them.

“You look at Bernardo now, who was absolutely terrific at the weekend. He’ll probably be the next £15m or £20m player to go from Celtic.

“He’s that good. Matt O’Riley was £1.5m from MK Dons a couple of years ago, you’ve got Kieran Tierney coming through from the youth team, Moussa Dembele who cost £500,000 and they sold him for £20m.

“It’s remarkable but it’s down to hard work from Brendan, his style and putting them in when they’re ready.”

Bernardo was one of several new signings during a busy transfer window for Celtic, along with Kasper Schmeichel, Arne Engels, Alex Valle, Adam Idah and Auston Trusty.

“I thought they covered most of the areas,” Hartson said. “They got a left back in, they got a centre back in. A central midfielder and Adam Idah in attack.