The 25-year-old left Sunderland at the end of last season when his contract expired and has since become an integral part of fierce rivals Newcastle's side.
And Quinn says it was 'undoubtedly a blow' for Sunderland to have lost the midfielder to the Magpies for free.
“I feel a bit for Gus Poyet,” the former Sunderland striker is quoted as saying by the Shields Gazette. “Losing Jack Colback was undoubtedly a blow.
“He had been a really strong player for Sunderland for three years. And we didn’t bring him through and work on him to make Newcastle stronger!
“He and Jordan Henderson have been the pick of our Academy players in recent years and we got good money from Liverpool for Jordan but to lose Jack for nothing certainly hurt.
“Something went wayward there. It’s a shame for us because he was just becoming the player we knew he could be.”