"It's definitely been tough," Cain said after pitching a shaky four innings on Wednesday in a 10-6 loss to the D-backs at Salt River Fields. "[Injuries are] something I think guys have to definitely deal with through their career. You hope you don't have to. I had such a long [healthy] stretch of not having to deal with it.
"For it to come in the latter part of a career definitely makes it difficult. You don't bounce back the same way."
Including Wednesday's seven-hit, six-run performance, Cain has thrown 6 2/3 Cactus League innings and has recorded a 12.15 ERA.
Yeah, there's all that stuff about veteran pitchers feeling their way during Spring Training and the stats don't matter, but the stark reality is that Cain might not be ready to open the season, so manager Bruce Bochy has a plan B.
Chris Heston threw behind Cain on Wednesday, and he could easily be slotted in Cain's fifth spot in the rotation.
"[Heston will] throw in another five days and give us some coverage there," Bochy said. "[Cain's] arm is healthy. It isn't his arm that set him back. It was that cyst. Still, it's Spring Training, and you've got to build up. The arm gets a little bit dead before it gets stronger.
"We'll see where he's at after the next start. I think the next start is going to be a critical one for him."
That next start could be on Monday in a Minor League game, Bochy said, and if that's the case, Heston would be on the mound against the D-backs instead of Cain on Monday night in the spring closer at Scottsdale Stadium.
It wasn't as if Cain looked all that bad on Wednesday, he just did some things that set off the alarms. Chris Owings skied his second pitch onto the left-field berm for a home run, and pinch-hitter Jake Lamb crushed a hanging slider onto the right-field grassy knoll for a three-run shot with one out in the fourth.
Cain had little movement or pop on his fastball, and the location on his breaking pitches wasn't particularly great, either.
Perhaps Bochy simply would rather there not be an audience the next time Cain pitches.
"We've already talked about that so we can monitor him," Bochy said. "That way, we can make sure we get the workload we need. That's a controlled situation for us. I think for Matty that might be important.
"It's not for sure, but that's the way we're leaning, to be honest. Heston would start in his spot, so we'll have him ready."
For Cain, amazingly, it has come down to all this. Along with Tim Lincecum and Madison Bumgarner, he was a member of a trio of starters that came up through the organization and, beginning in 2010, turned the Giants into three-time World Series winners.
Lincecum is gone after hip surgery, and his career might be finished at 31. Cain, also 31, had his 2014 season end at the All-Star break because of surgery to remove bone chips from his right elbow. He missed 94 games last season because of a flexor strain in his right forearm and nerve irritation in the surgically repaired elbow.
Cain has never been the same.
Because of the cyst removal, Cain didn't make a spring start until March 18. He says he's healthy now, healthier than he has been since mowing through the 2012 season with a 16-5 record and a 2.79 ERA in 32 starts. Cain has won only 12 games since then and has made 26 starts the past two seasons.
All that can cause a dip in confidence. It happened to Lincecum despite two National League Cy Young Awards, two no-hitters and three World Series rings. By midseason in 2015, his confidence was shot.
Cain can relate.
"It's tough, because it's something you've never had to deal with," Cain said. "You're used to making your start every five days and competing along with the rest of the team. It's part of being on the disabled list. You feel like you're the extra guy on the team. You've got to try to find ways to get better. Things change.
"You've got to start working with the things that you have and start trusting a lot of how it feels. Not try to panic too much."
The Giants can only keep hoping. They have Cain under contract through 2017 at $20.83 million per season, plus a $21 million club option for 2018 with a $7.5 million buyout.
The option vests if Cain pitches at least 200 innings in 2017, 400 innings between 2016-17 and isn't on the DL with an elbow or shoulder injury at the end of the 2017 season.
Perhaps that's why Bochy has this modest expectation for Cain this season:
"To make his starts," Bochy said. "Make his 30-plus starts. And have a lot of those starts be quality starts and give us a chance to win. That's all I want from my starters, and that's what I expect from Matty."
Considering what has happened to Cain the past two seasons and where he is right now, that would be above and beyond what anyone might imagine.