Casiraghi, who has been undergoing rehabilitation treatment in Italy for six hours every day, will not play again until well into next season, by which time there is likely to be at least one more Italian striker rivalling him for a place. Indeed, it is possible that the failure to replace him as soon as the extent of his knee injury became known lies behind the near-collapse of a season that promised so much.
With eight minutes of the Leicester game remaining, there was everything to play for. Chelsea had confounded the gloomy prognostications of their player-manager Gianluca Vialli by recovering from an unexpected home defeat against West Ham to steal back on to the shoulder of Manchester United and Arsenal. Beyond that lay the second leg of the European Cup-Winners' Cup semi-final in which Chelsea had been favourites all season to come through a poor field and meet Casiraghi's old club in the favourable environment of a Villa Park final.
Suddenly, however, the weariness that Franck Leboeuf and Marcel Desailly, the World Cup winning centre-backs had felt intermittently ever since their exploits last June caught up with them and, aided by Vialli's self- confessed tactical error in persisting with an unfamiliar 3-5-2 formation, Leicester were able to pull back two goals and change the look of the Premiership chase.
In Palma four days later, the prospect of retaining the Cup- Winners' Cup vanished largely because - despite all the untiring excellence of Gustavo Poyet, whose knee injury on Boxing Day permitted a much quicker recovery than Casiraghi's - Chelsea had run out of genuine goal scorers. From 22 shots (to Real Mallorca's eight) they could not hit the net.
As an impressively - almost extravagantly - large first-team squad posed for the official pre-season photograph last summer, such a possibility seemed impossible to contemplate. The question then was how Vialli, determined to play a leading role himself, could possibly keep all his other strikers happy, even over a demanding eight months. There alongside him in the front row were his compatriots Gianfranco Zola and Casiraghi; behind them stood Tore Andre Flo and another expensive new recruit, Brian Laudrup. Goals, it was assumed, would not be a problem.
Compare that picture to one of the Chelsea substitutes bench on Thursday as Mallorca's famed defence repelled the best that Flo and Zola could throw at them. Just when an extra striker was required to step from the dug-out, there was Vialli sitting in his civvies ("I could have risked myself but decided not to. I'm not the sort of player who can come on and turn a match") alongside a crop of defenders and midfield players.
Casiraghi was at home, no replacement had been signed, and Laudrup was long gone. His last contribution to the Cup-Winners' Cup run having been to ensure a place in the quarter-final by scoring the goal that knocked out FC Copenhagen, the club he was about to join.
The disappearance of his pace - an increasingly important quality in the modern game - has shown up Chelsea's deficiencies in that area. It is something they need to address as a priority in planning the changes that must follow if the season is to become part of what Vialli sees as a progression towards real success. "We've improved in the League, which was our most important target this season," he said. "To see an improvement is the most important thing for a manager."
Keen as he is to keep playing, the 34-year-old's acknowledge-ment that he can't do so for ever is a reminder of the squad's advancing years. Astonishingly, the average age of Thursday's team was 30, with Flo the only player under 28. As Chelsea set out to retrieve a Champions' League place from last week's wreckage, beginning at Sheffield Wednesday this afternoon, that is hardly a base for any sort of long-term success.