Tierney took Izaguirre’s place in the Parkhead club’s first team when he broke through in season 2015-16. But the Honduran holds no grudges.
He left Celtic to join the Saudi Arabian club Al-Fayha last year with Tierney firmly established as first choice.
Izaguirre’s move to Saudi did not work out and he was delighted to come “home” to Celtic yesterday.
“I am happy to be back because this is my home,” he said. “I played seven years here so it is good to be back in Scotland.”
When Izaguirre first met Tierney the former was a World Cup star and the latter was an impressionable 13-year-old wannabe.
The Honduran had just been signed for Celtic for £650,000 from Motagua by then manager Neil Lennon while Tierney was working his way through the ranks and savouring his first taste of the big time as a ball boy.
It was a case of master and pupil as devout Christian Izaguirre offered advice and encouragement to his apprentice while also acting as a role model in the way he comported himself away from the training ground.
Tierney was a quick learner, to the extent that he had effectively taken the older man’s place in the team during 2015-16, Ronny Deila’s final season in charge.
“I have no problem that Kieran is the left-back; maybe I can get a chance, but no problem,” said the 32-year-old.
“I said before that Kieran was my boy. He tried to learn from me and I tried to learn from him. I saw him grow up and up for five years and I’m happy to see him do well.
“Now I want to see him become the best left-back in the world. Can he do that? Of course. He has lots of talent and just needs to focus and he can do it.
“I can help him. I remember in 2015-16, when he played his first game, I tried to tell him never to stop working hard – ‘keep being professional and you can be the best one day.’
“He has the talent and I spoke with him about always working hard. Football is about talent but it’s more important to be professional.
“I am 32 years old, but I’ve stayed strong and fit. It’s like Scott Brown. Be fit and be professional and you can keep going.”
Izaguirre revealed that he and Tierney remained in touch after the former’s departure.
“We kept speaking after I left,” he said. “He texted me and I texted him and we spoke again this morning.
“We always kept positive and I’m happy to see him be one of the best; it gives me pride to see him do well. I remember in 2010 when he was very young. He gave me his hand to shake and he was following me.
“I see him now and he looks physical. Two years ago, I told him go to gym, run every day. He did that last season after training every day.”