Bumgarner dismissed the sensation in his chest as "just something slight." Asked if anything was wrong with his oblique, he replied, "Zero."
The level of manager Bruce Bochy's anxiety registered at slightly higher than zero.
"There's always a little concern when a guy misses a start," Bochy said. "But I'm staying optimistic that he'll be OK."
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Bumgarner's woes were the latest instance of bad luck to befall San Francisco's projected starting rotation. Right-hander Johnny Cueto, who signed a six-year, $130 million deal to serve as the Giants' No. 2 starter behind Bumgarner, missed his first scheduled spring assignment because he needed more time to build arm strength. Right-hander Matt Cain still hasn't appeared in a Cactus League game as he recovers from removal of a cyst on his throwing arm.
Bumgarner, who has exceeded 200 innings for five consecutive seasons, expressed hopes of returning to the mound as soon as possible. But the Giants' medical staff didn't announce a timetable for his recovery.
"It'll probably be only one [missed start], but they're saying one or two, just to be safe," said Bumgarner, who's confident he'll regain enough stamina to start the season opener. "It's not anything too serious, but we just don't want to turn it into something serious."
Bumgarner, 26, has pitched this spring despite the pain in his foot, which he said began to nag him "sometime in the offseason."
Asked to describe the feeling in his foot, he said, "Well, I mean, yeah, it hurts. But it's just kind of hit or miss. Sometimes it does and sometimes it don't. It's not like a typical nerve injury where it's all the time."
Bumgarner added, "It's getting better. It's making a lot of progress, actually. I've been pitching with that. That wasn't really the issue. I just don't want to have two things going on."
Yet the combination of maladies was annoying enough to sideline the three-time All-Star and 2014 World Series Most Valuable Player.
"There's just no sense in trying to pitch through something like that and taking a chance," he said. "It's just Spring Training. It's probably not going to hurt to miss a start or two."