Paul Hartley in Celtic Champions League warning as he makes case for a plan B on the continent

Paul Hartley was part of a Celtic team that qualified from a Champions League group containing AC Milan, Benfica and Shakhtar Donetsk.

A year later he was in the side that failed to progress from a quartet that included Manchester United, Villareal and Aalborg. Fair to say then that the former Hoops star is a good judge of what lies ahead as Ange Postecoglou ’s troops prepare to take their first steps back into the group stage of the competition for five years.

And when he warns that the challenge facing them will be even more difficult now than in his time then it’s time to listen. Not only has the financial gap between Europe’s haves and have nots expanded in the 15 years since Hartley was strutting his stuff in Gordon Strachan’s side. But the game in general has moved on too with the top sides producing the kind of fast, free-flowing, attacking football that makes you scared to blink in case you miss it.

Having to change your approach from the bread and butter fare of the Scottish Premiership to tackle the cream of the continent is nothing new. But Hartley insists it’s crucial when it comes to trying to plunder points on the big stage.

And while Postecoglou is on record insisting he will never compromise on his footballing principles - no matter the cost - Hartley reckons the megabucks on offer for Champions League progression Hartley might just convince him to rein it in a little. Especially on the road.

The Hoops’ record in the group stage during the 45-year-old’s two years in the east end of Glasgow makes for stark reading when it comes to trying to topple the giants on home soil compared to foreign turf.

In the two successive group stage campaigns in 2007/08 and 2008/09 not one of the six home games were