Cain, 28, has never before been on the DL in the big league career. He's been a 32+ start, 210+ inning workhorse for San Francisco since breaking into the league full-time in 2006.
In 26 starts this year, Cain has a career-worst 4.43 ERA (75 ERA+) and 2.98 K/BB ratio. He does, however, have a 3.51 ERA in his last 14 starts after pitching to a 5.45 ERA in his first dozen outings.
The Giants are 56-71 and in last place in the NL West, so they have every reason to be extremely cautious with their franchise pitcher. Cain is in the first year of a five-year, $112.5 million contract extension.