“There’s a popular misconception that any professional baseball player who spends even one day on a major league roster will receive free health care for life. In reality, that’s not true. Instead, what one day of service gives you is the right to buy into a healthcare plan, which isn’t really the same as free, comprehensive coverage. A player’s eligibility for health and pension benefits is tiered, and depends on how much time the player spent on a major league roster, how much service time he accrued, and can even be a matter of which years he played, as different benefits are available to different eras of players. Different plans carry different co-pays and have varying coverage maximums.”
https://blogs.fangraphs.com/micah-bowie-player-benefits-and-another-front-in-labors-fight/