The story has gotten a lot of play since Saturday night but the issue remains, Ethier has had an knee issue all year and it finally began to really bother him on the last road trip.
It is fairly well understood that professional athletes are almost never 100% healthy. With the toll of the regular season, you are going to get your share of bumps and bruises during the year.
Ethier does have a bonus in his contract for reaching 600 and more plate appearances, at 600 and 625 PA he gets $25K and at 650 he gets $50K. With 30 games left, he would have to play them all to get to 650 PA but that would be an extra $100K for Ethier. Teams have been accused of holding players out when they had certain incentives in place (famously, Eddie Cicotte of Black Sox fame was allegedly skipped at the end of a season when he had a chance to reach a performance clause).
The CBA is not all that clear on what teams can do when a player is hurt. They can examine the player and give a medical opinion. The player has the right to request a second opinion. But I cannot find a definitive understanding of whether the team or the player can decide how and when an injury gets treated.
I don't think the Dodgers can just arbitrarily just not play him, if Ethier says he could play, he would certainly file a grievance with the MLBPA to force the team to change its mind. They could disable him if the medical staff sees fit but again, Ethier could request a grievance if he believes he is not hurt.
I suspect the Dodgers, Ethier's representatives, the MLBPA and Ethier will try to come to some understanding. But it is not cut and dry and certainly not as simple as just deciding to disable Ethier.