The disappointment etched on Neil Lennon's face after Wednesday's loss at the Juventus Stadium could not solely have been on account of Celtic's Champions League elimination. The seeds of that, after all, had been sown in Glasgow three weeks earlier.
Rather, there will be a realisation from Lennon that he has probably watched a talented batch of young players compete together against Europe's elite for the last time.
Celtic have managed to retain Victor Wanyama, Gary Hooper and Fraser Forster thus far, largely because of the team's Champions League exploits, but by Lennon's own admission his key players are already glancing towards England. Crucially, it is not all one-way traffic. For all that Celtic's most recent recruitment drives have been highly successful, the focus afforded on such players by achievements against high-quality opposition has been hugely significant.
Lennon himself is factored heavily into this equation. Like his players, he has proved how possible it is to turn heads by virtue of European performances. Such attention is not received, rightly or wrongly, because of what any Scottish team achieves on their domestic front.
The likelihood, therefore, is that Lennon will also be the recipient of overtures in the summer. His decision at that juncture would be whether to stick with the challenge of rebuilding his team and progressing the careers of the young talent at his disposal – James Forrest and Adam Matthews among them – or move on at the point where his ticket is hot. Both options will appeal, but both carry dangers for a manager who has proven his knowledge of tactics and personnel.
Celtic will be assured of Scottish Premier League dominance for the foreseeable future but that, in itself, carries a sense of monotony and, to a degree, a potential lack of fulfilment. The club's season ticket sales and SPL attendances next season are already a source of intrigue.
European nights, while wonderful occasions for Celtic, are offset by mundane trips to the likes of St Johnstone or Inverness. The prospect of a farcical shake-up to the SPL, possibly as early as next season, should do little to enhance its appeal either. Just as players want to use Celtic as a stepping stone to a superior league, such as in England, it is only logical to assume Lennon has aspirations of a loftier platform. And yet it is legitimate to argue whether that means a mid-table or relegation-threatened club in England.
Lennon endured the most nervous times of his managerial career as Celtic negotiated the qualifying stages of the Champions League. During the intervening seven months they have won in Moscow, lost in the cruellest of fashions at Camp Nou and beaten Barcelona in Glasgow. Although Juventus were comfortable 5-0 aggregate winners in the last-16 tie, Celtic will and should receive high praise for their positive approach. Ultimately, a gulf in class was obvious.
There have been heroes in green and white along their impressive journey. Celtic's blue chip trio aside, Georgios Samaras has matured into a reliable performer in big matches. Kelvin Wilson excelled against Juventus while Charlie Mulgrew's set-play delivery is as potent a weapon as any European team possess.
Now, however, the run is over and the end of the Celtic road is also fast approaching for certain players. They are worthy of that prominence; the challenge for the club is to return to the European level which they have relished since last summer.