Sutton and Douglas played together at Parkhead for several years and were a part of the Hoops side which famously won the domestic treble in 2001, and reached the 2003 UEFA Cup Final in Seville.
However, Douglas was often dogged by high-profile goalkeeping errors – perhaps most notably in that 2003 final against Porto.
But Sutton has revealed the ex-Scotland international was constantly being told off by O’Neill, particularly at half-time in certain games.
Speaking as a pundit on BBC Radio 5Live’s Monday Night Club in regards to the furore surrounding current Liverpool keeper Loris Karius, Sutton explained: “It’s about a manager working out whether to put an arm around a certain individual or to be tough on them.
“Martin O’Neill, my old manager at Celtic, was always pretty tough on, well, not just goalkeepers, he didn’t just keep it for the goalkeepers.
“But he used to batter Rab Douglas and Jonathan Gould at half-time. Quite rightly, most of the time!
“And I used to wonder how they went out and played in the second-half. That was his style.”
Sutton’s little insight into the workings of Celtic’s goalkeeping department in the early 2000s didn’t stop there.
Later in the show, when fellow pundit Robbie Savage explained how tough it was training on a daily basis to be a goalkeeper, Sutton interjected, saying: “That didn’t happen at Celtic. They used to do a few 20-minute half-volleys then go in and have a pie!”
We expect he was joking with that last comment, but Sutton’s comments on Douglas offers an interesting insight into O’Neill’s reign in Glasgow – and the Englishman’s take on Douglas’s performances.
What do you make of Sutton’s comments on O’Neill and his approach towards goalkeepers at Celtic?