The only saving grace for one of the finest Scottish players of his generation, whose career has been ravaged by serious injuries, is that the damage has not, this time, been deemed serious enough to require surgery.
He is expected to be out of action until mid-December and, while his absence is covered by the growing strength in depth of the squad, it is a blow for both club and country. Andy Robinson, Scotland's head coach, observed: "It's disappointing for Chris because he has made such a good start to the season. I wish him a speedy recovery."
One man's disappointment in sport is always another's opportunity, though. In this instance, the timing is propitious for Henry Pyrgos since, starting with tonight's meeting with Connacht, it lets him re-establish himself before Niko Matawalu, the club's Fijian signing, turns up, if and when he does after a lengthy hiatus since his recruitment was announced in July.
The latest bulletin indicated that Matawalu is expected to be in Glasgow this weekend, his visa having come through. However, once he is in camp, Pyrgos will make him fight for his place and the Scotland A cap noted that his readiness to do so is a measure of the intelligent way he was managed last season. Then, the promise made to him during his rookie campaign in 2010/11 – that he would spend much more time on the pitch the following season – was held to. "The longest run I've had was at the end of last season when I got four or five games and felt I played really well," said Pyrgos.
Given Glasgow's paucity of resources at that time, it was inevitable that Pyrgos would play when Cusiter was away on Test duty or injured, but the faith shown in him at key stages reinforced his self-belief. "That was a big step for me," he said. "I felt I had a good chance and I improved and we got a lot of good results there, so that was a good period. Any chance I get I've got to keep kicking on and doing what I can."
That is something every professional player has to aim to do, but there can also be a danger in trying to bring about change through revolution rather than evolution and the impression that senior players had, after losses on the first two Pro12 weekends, reasserted Glasgow's core values ahead of last week's visit to the Ospreys was in no way contradicted by Pyrgos's account.
"I didn't really feel we got our attack going as we would have wanted, but a big thing for us is our defence," he said. "We defended really well and the tight five were brilliant, working really hard, putting in tackles and getting back up on their feet.
"Obviously, another big thing is not beating ourselves and I thought we did that really well. We didn't give away silly penalties when we didn't need to and, in the first half especially, we didn't concede points when we didn't need to."
It was certainly a contrast with their other away match this season when recklessness in attack – something that has been more of a feature of Scotland's play than Glasgow's in recent years – played a huge part in letting a callow Ulster back division decide the outcome.
Those who generated that winning culture at Glasgow are all the more aware that they must reassert those values because, if they are not performing effectively and lose their places, they may be out for a while such is the depth of squad the club now boasts.
That has been reinforced by the experience of another of their half-backs, since Ruaridh Jackson has gone from being seen as new coach Gregor Townsend's preferred first-choice stand-off when he started against the Scarlets two weeks ago, to the bench last week and now to Scottish RBS Premiership rugby, with Ayr.
Townsend said this week that Jackson had not taken that as a slight and is looking forward to the game time he will get, but it is not a sequence of appearances that any other contender for a place in Scotland's autumn Test squad will be eager to follow.