McCormack, who rose through the ranks at Ibrox, played alongside the Celtic loanee at Fulham.
McCormack celebrates scoring for Fulham
McCormack, who grew up a Celtic fan, quit the Light Blues for Motherwell in 2006, before embarking on a successful career south of the border.
McCormack in action for Rangers against Anorthosis Famagusta
Now of Fulham, the 29-year-old finished as the Championship's second top scorer last season, prompting interest from relegated trio Newcastle United, Norwich City and Aston Villa according to reports over the bank holiday weekend.
And drawing on his own experience while discussing the future of Celtic's on-loan Manchester City winger Patrick Roberts - with whom he played at Craven Cottage last season - McCormack suggested that securing regular matches is key to any young player's development.
"When he (Roberts) signed for Celtic I knew he would do well because he has always had the ability to go past players like they are not there," McCormack said, as quoted by the Glasgow Evening Times.
"But when he develops into his body and gets stronger and starts to learn the game a bit more the sky is the limit for the kid.
Roberts in action for Celtic against Rangers
"I struggled to get a regular game at Rangers during my time there. I enjoyed being at Ibrox, but it was important for me to play week in, week out and I definitely improved when I moved on and started to do that."
McCormack, who has 12 caps for Scotland, scored four goals in 14 appearances for Rangers, but was released despite this - along with a successful stint at Doncaster Rovers.
The Glaswegian later enjoyed spells at Cardiff City and Leeds United, who sold him to Fulham for a reported £11 million two summers ago.