Strachan, who succeeded O’Neill at Celtic in 2005, has previously told BBC Sport of working at Parkhead: “It's great, don't get me wrong. I do believe if you can manage Rangers or Celtic you can go on to become Prime Minister of Great Britain. I think it's that hard.
“You only get to enjoy it for about 24 hours at Celtic, because there's always another crisis just around the corner. So you have to be aware of that. You would imagine you get a lot of time to enjoy it, but you don't at Celtic. But what it is, is one of the best clubs in the world to manage and you have to deal with the rest of the stuff.”
O’Neill has learned over the years how to handle those demands - having also spent time in charge of Leicester, Aston Villa, Sunderland, the Republic of Ireland and Nottingham Forest. He told Sky Sports of having to prove himself again as a pensioner: “The first time that I went back it happened so quickly, Brendan had resigned, I get a call the same afternoon to ask if I would come up and hold the fort.
“Naturally I was worried about it. The reason I was worried about coming back the first time round was that if you don't win, you're just considered old, you're just too old.
“It wasn't about whether you were going to ruin anything you did a load of years ago but at the end of it all, it was just that you would be considered just too old and you're not in the new game.
“And then [for the second spell] I get a call, asking to come in now to the end of the season. My worry then was, yes, it's a wee bit longer this time, we've ground to catch up again and I suppose I had the same fears and worries about it, whether we can do it, because games start to run down.”