Bolger, a product of Leicester City's youth academy, was one of Dougie Freedman's first permanent signings, joining the club on deadline day in January 2013 alongside Medo Kamara. The 21-year-old centerback went immediately into the reserve team and was named captain of the U21s soon after. Bolger featured regularly in Bolton's pre-season preparations.
The central defender, an Ireland U21 international, was handed a professional contract with the Foxes in 2010. During his time at Leicester City, the 6-foot-4 Bolger was sent out on loan to Bristol Rovers on three separate occasions. It was there that Bolger made his professional debut, making 49 total appearances for the Gas. The third stint, originally meant to be a six-month loan, was interrupted after Bolger suffered a cruciate ligament injury. He would make his return three months later, facing the team that he suffered the injury against.