When Julien Stéphan celebrates his anniversary as Rennes head coach on December 3, he will have the opportunity to look back on a year of two halves.

Plunged into the role with a side suffering what appeared to be an interminable downward spiral, he stepped up from his duties as reserve-team boss to lead them immediately to an entirely unexpected victory over Lyon. It was the foundation of a five-match winning streak in the lead up to Christmas that profoundly changed their fortunes.

From there, Rennes won the Coupe de France, defeating Paris Saint-Germain in the final, and earned plaudits for their European performance, which saw them shake the shackles of the stereotypically cautious French approach with a barnstorming victory over Real Betis is Spain before a narrow exit to Arsenal, having defeated the Premier League side at Roazhon Park.

Season 2019-20 is proving to be more testing, however.

Notoriously poor in European group stages – Rennes have won only four of 28 fixtures at such a juncture – they have reverted to type after their thrilling spring displays, while a promising start domestically, including another win over PSG, has given way to mediocrity of late.

Saturday’s 2-1 defeat away against Dijon, however, provoked a particularly passionate outburst from the coach.

“We missed everything,” he lamented after seeing his team overhauled by the relegation strugglers in the final 20 minutes after Raphinha had given them the lead. “I’m ashamed of the display we produced. We had nothingness in almost all areas.

“It’s a big warning. Of course there’s anger, but there also a lot of worry.”

Stéphan built enough credit last season to ensure there is no immediate threat to his job, despite the club being only three spots better off than when he took charge, but there is little doubt things are not going quite according to plan.

Injury problems have hampered the Breton side throughout this season, with leading league scorer Mbaye Niang having been plagued by knee trouble, while fellow forward Adrien Hunou has only regained fitness in the last month after an early-season issue.

Dogged by such worries and already having seen their hopes of European progression extinguished, largely thanks to two incredibly unfortunate defeats against Cluj, the side that has travelled to Glasgow is not at its full strength.

Niang, widely recognised as their most dangerous scorer, has been left in France to nurse the problem that has prevented him from reaching his peak this season, while the ongoing absence of industrious central midfielder Jonas Martin is one that will weigh heavy on the team.

Undoubtedly the greatest loss from the team, however, is that of 17-year-old sensation Edouardo Camavinga.

The greatest talent to burst onto the Ligue 1 scene since Kylian Mbappe lit up the league with Monaco in 2016, the Angola-born central midfielder is a player with the maturity and class of a player a decade his senior.

Even before he debuted for Rennes as their league campaign wound down to a forgettable end last season, becoming the club’s youngest player in the process, there was a tremendous buzz around France over his talent. This was simply confirmed as he established himself as a starting player as the campaign concluded.

Following a spectacular start to the current season, in which he has been Rennes’ outstanding figure due to his technical ease and all-round ability, France scrambled to naturalise him and gave him an Under-21 debut against Georgia on November 11, less than a week after his citizenship was confirmed.

A thigh injury sustained during the warm-up for the following encounter against Switzerland last week has, however, kept him out of the trip to Glasgow and deprived Celtic fans of watching one of the world game’s greatest prodigies.

Rennes, who have eight games to play in the space of 24 days, are therefore liable to field something of a fringe side in Glasgow.

Winger Flavien Tait is one to watch, though he is another to have been trouble by physical issues since signing from Angers, where he was one of the French top flight’s most under-rated performers. He only made his return to action after six weeks out with a half-hour cameo at the weekend.

Rennes youth academy, meanwhile, is consistently ranked among the best in France and, indeed, Europe.

While the likes of Brandon Soppy and Georginio Rutter are ultimately expected to follow Camavinga into the first team, the best positioned prospect to make an impact on Thursday’s fixture is 18-year-old midfielder Yann Gboho, who has recently broken into Stéphan’s plans.

Listed as a midfielder, he has been used in a more offensive role for the first team. He grabbed a stoppage-time winner in a recent win over Toulouse having been introduced literally seconds earlier.

If Stéphan and his side take anything from Thursday’s fixture, it would be an unexpected bonus. The best anniversary gift that the coach could wish for is, instead, maximum points from the forthcoming league matches against Saint-Etienne and Metz.