Celtic have tried to sign Hearts' Aaron Hickey "five or six times", says former Tynecastle manager Craig Levein.
Hickey, 18, is in the final year of his contract at Hearts and has attracted interest from Bayern Munich, Aston Villa and Bologna.
The former Celtic youth player can play full-back and in midfield, with Hearts valuing him at £1.5m.
"Celtic tried to buy him back half-a-dozen times and that just got knocked back," Levein told BBC Radio Scotland.
"Celtic tried to buy him back while he was in the first team, I think it was five or six times."
Hickey has made 33 appearances for Hearts, scoring once, and the Tynecastle side, who have been relegated, begin their Scottish Championship campaign in October.
And Levein, who was previously Hearts' director of football, added on Sportsound: "He's got really good defensive qualities. He likes defending, which is a rare thing these days.
"He might end up going back into the midfield area. I think he'd be a fantastic holding midfield player with his great awareness of danger and his ability to get out of tight situations with the ball at his feet."