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From 2019/20, English Premiership Rugby is seeking to put in place a new domestic season structure running from September to June, in part to allow its clubs to not play matches on Six Nations weekends.
With international tours then switched to July it means potentially only a maximum four-week break for players in a sport where rest and recuperation and welfare has become the hottest of topics.
The RPA was not consulted over the proposals and several players, including England duo Billy Vunipola and Ben Youngs, have raised the idea of strike action if they are forced to accept such a short off-season.
"The fact you've had a number of players speaking out unprompted just shows you the strength of feeling amongst the players," said Hopley, speaking at the Leaders in Sport conference in London.
"We were very disappointed that the league didn't engage us at all about this - it was presented as a fait accompli. Strike action is obviously an option and it's the ultimate sanction but there's enough common sense and grey hair around the table to try to find the right solution."
Hopley's comments came on the day The Times newspaper published Opta statistics showing a substantial rise in injuries in the first five games of the Premiership season, possibly linked to a marked increase in the number of rucks and tackles - where the vast majority of injuries are sustained - following law changes introduced this season.
"It's a big concern, the players are going down in droves," Hopley said. "We talk a lot about anecdotal evidence but to see the rise in tackles and rucks...in many ways our players are the guinea pigs and the injury count is higher."
Clubs' representative Mark McCafferty has previously dismissed player concerns, saying that they were based on not understanding the proposals. His contention that the players would get more rest in periods during the season was rejected as irrelevant by Hopley, who said the mental as well as physical load of playing, or being primed to play, for 11 months needed to be taken into consideration.
"It's about asking the sports science and medical experts to come up with what an optimal season looks like," he said. "We should start with the off-season and go from there.
"Five weeks into the Premiership season the quality has been through the roof - it's just whether that's sustainable. I think we're all crying out for less, rather than more, at the moment."
The issue will be top of the agenda when the Professional Game board - with representatives from the RPA, the Premiership, the Championship and Rugby Football Union involved - meets in November.
"We have to sit round the table and try to thrash out what will work, with player welfare not actually being talked about, but actually being acted upon," Hopley said.