Hay not only made over 100 appearances for Celtic, but returned to Celtic Park as the club's manager in 1983, spending almost four years in charge of the club.
Today, he told the Glasgow Evening Times that he's been hugely impressed with midfielder Scott Brown, who is out of contract in 2015.
"Scott is already one of the club's top earners, and is playing the best football of his career after finally shaking off the injuries and personal issues which marked earlier years at the club."
"This has not gone unnoticed down south, and Scott will have a very good idea what he could be earning in the Premier League. With his energy and skill, there is no doubt he could do it at a Sunderland or Newcastle," Hay said.
That's already high praise for the 29-year-old who joined Celtic from Hibernian in 2007, and after almost 300 appearances for the Hoops, he's earned plenty of plaudits for his aggressive, never-say-die attitude - and Hay says he should be a target for Liverpool and Manchester United.
"But, such has been the improvement in him, both for club and country, I could even see a case for suggesting that a Liverpool or Manchester United might see something in him that would appeal to them," added Hay.
Brown's energy and commitment would be valuable for Newcastle if they lost Cheick Tiote, but partnering him with Lee Cattermole at Sunderland would be verging on catastrophic.
As for Liverpool and Manchester United? Well, Brown making the move down from Scotland and immediately to one of the biggest clubs in the Premier League would be a great story, but is also massively unlikely.
Brown has the heart and desire for success, but his technical ability isn't really up to the high standards of Liverpool and Manchester United.
Adored by the Celtic Park faithful, Brown should be doing everything within his power to stay at Celtic for the foreseeable future - though a move to a Premier League club could be appealing with his contract running out next summer.