FR Liam McClarey, our team chaplain when we won the All-Ireland in 1993, had an audience with his Holiness the Pope in Rome last Thursday.

Liam played on the Glack team that won the Derry Junior Championship in 1981. The competition is called the Joe Brolly Cup (after my late grandfather) and as my father said after the game when he presented the cup to Glack’s captain Chris Devlin, “It’s hard to believe your full-back is a priest.”

For his audience at the Vatican on Wednesday, Liam wore his Derry tracksuit, or his “Sunday best” as he calls it. My brother Proinnsias likewise wears his Derry tracksuit top for good occasions. As he says, “it saves you the bother of picking an outfit.”

When he was ushered into Pope Francis’ presence, Fr Liam, who is head of the Palatine Order in Ireland, presented His Holiness with a painting commemorating the five palatine priests who were murdered by a right wing death squad in Buenos Aires in 1976. He then got down to business, and inquired of a bemused Papa Francis if he thought Donegal could beat Derry in Celtic Park this Saturday. Francis wasn’t familiar with the issue, so Fr Liam had to make do with asking him to say a prayer for the Derry boys. “I’m surprised he doesn’t get GAAGO,” Liam said when we chatted on Thursday. “Maybe he can’t afford it,” I said.

From a long way out, these two teams have been arrowing towards each other. Jimmy McGuinness fascinates the GAA public in the way Harry Houdini used to fascinate his audiences. In 2011, when he turned Gaelic football on its head and ended up getting booed out of Croke Park after the semi-final against Dublin, the weirdest and worst game ever played, we thought that was the end of him. But like Wendy in the Shining, we just didn’t understand.

The crowd in Croke Park that day and the millions watching around the world were open mouthed as Donegal’s entire 15 retreated inside their 45. Then enraged. Then fearful. Donegal lost 0-5 to 0-7. We thought Jimmy was publicly shamed and humiliated. The truth was that Jimmy was thrilled. His experiment had been a success. All he needed was to tweak it. He left Croke Park that day thinking “I know how to win this now. I know how to win it.” That very week, he drew up a new blueprint, and 12 months later they trounced Mayo to win it all, having trounced everybody else en route.

We know some of the stories. When he met the Donegal squad for the first time in 2011 in a hotel in Downings, they were bemused when each man was presented with a typed behavioural contract drafted by a solicitor. The agreement was described as “legally binding” and contained penalty clauses. The force feeding of Rory Kavanagh, turning him from a 12 stone wing forward into a 14 stone midfielder, his face appearing at the Kavanagh’s kitchen window late at night like Freddie Kreuger, checking he was eating his bed time tub of ice cream.

Icily banishing his All Star wing-back Kevin Cassidy before the 2012 season for telling a journalist the story about Jimmy confiscating the players’ phones on the morning of the 2011 semi-final.

Now they’ve installed a 15 feet high privacy fence around the Donegal training pitches at Convoy. If Donegal get to the Ulster final, they have plans to increase security by adding a moat and a secure area around the perimeter patrolled by dobermanns. With Jimmy, you just never know.

He is Gaelic football’s Rasputin. The Dark Lord of strategy and psychology. With those flashing eyes and absolute conviction, he brainwashes his players. Hypnotises them. Soon, Jimmy’s ambition becomes their reality.

In 2011 he climbed into Mickey Harte’s head and hasn’t been out of it since. He told his bemused squad of losers before that season that they would win Ulster, then Sam and they would start by “breaking Tyrone”. So, they worked obsessively towards that goal, endlessly studying Tyrone’s manager, players and method of play.

Six months later, they suffocated Tyrone in the Ulster semi-final, not just beating them by three points but demoralising them and stripping away their aura. Twelve months on, in the 2012 Ulster semi-final, another merciless beating. Mickey got a third chance the following summer, but by then the life was gone from Tyrone and Donegal cantered to a facile six-point win in the first round. Just as he swore he would, Jimmy had broken them.

Saturday’s game is a different matter. Harte may be the manager now, but Derry’s game-plan and evolution has come courtesy of Rory Gallagher, who was, with Jimmy, the co-inventor of modern football.

Like Jimmy, Rory is an obsessive and relentless perfectionist. Under him, Derry have gone from Division Four to Division One in successive seasons. Audacious game plans. Original ideas. Lung-bursting running. Intensive man to man coaching. Derry, unlike that Tyrone team, have not won the All-Ireland, so are voracious.

Vitally, our progression through all four divisions means that the group is entirely humble. When you have so recently played London and Leitrim in competitive football, you have a deep appreciation for the good times.

Also, we have lost two All-Ireland semi-finals in a row and suffered the terrible pain of leaving last year’s behind us. The league final performance proved to the boys they are capable of competing at the highest level. But it was the boys’ reaction at the final whistle that proved they are not going to be distracted. No jumping about. No celebrations. No big home coming night. Just hand shakes and talk of getting ready for Donegal.

If anyone else were managing Donegal, I would say that we would beat them comprehensively. But it is not anyone else. It is Jimmy McGuinness. This is the most important test this Derry team has ever faced. Win and we will be on our way towards a monumental All-Ireland semi-final. Lose and Jimmy McGuinness will be in our heads. Not even a papal prayer can exorcise that.