The former Sharks scrum-half is suing the club for alleged clinical negligence over a concussion injury.
"It puts club medical staff and doctors in a very, very difficult situation," Exeter director of rugby Rob Baxter told BBC Sport.
"If a player can suddenly turn around and start suing a rugby club, at what stage will it stop?"
Baxter added: "I think the majority of past concussion situations have been dealt with very professionally and very well.
"My big concern is, are we going to create - if we are not very careful - a scenario for our medical staff where they are almost having to drag players off the field just in case? That's the big worry for me."
Saracens director of rugby Mark McCall said: "If you put yourself in the shoes of the medic, it's almost an impossible job. Would they want to return someone to the field of play if they have been taken off for an assessment now?"
In 2014 the head injury assessment (HIA) was introduced, replacing the shorter and less comprehensive pitch-side concussion assessment (PSCA).
Any player who has suffered a head injury must have an HIA to determine whether they are fit to return to the field of play.
But McCall feels teams should be able to bring back on players who have been substituted on tactical grounds, in the event of a replacement suffering concussion.
"For us coaches there is the possibility of being reduced to 14 men because a sub fails his concussion test," said McCall.
"That is a ludicrous state of affairs. We want player safety, but it should be like a blood bin and we should be able to bring a replaced player back on the field and make sure teams stay at 15."
Baxter added: "Everything is so grey, that to really protect yourself, you could easily see 10 HIAs in a game. We just have to be a bit careful about where it will end up."
Wasps boss Dai Young said: "The Willis case could set a dangerous precedent. Let's hope it doesn't go down that path, but we all have total trust in our medics.
"We are all fully aware of concussion, but it is putting a lot of pressure on our medics now, and putting them under the microscope."
Subscribe to the BBC Sport newsletter to get our pick of news, features and video sent to your inbox.
Premiership bosses have said Cillian Willis' legal action against Sale could have wider repercussions for rugby.