San Diego manager Bud Black told reporters Friday morning that Latos will not make his scheduled start on Saturday.
That would have been the final Cactus League appearance for Latos, who appeared to be on track to start in the season opener in St. Louis on Thursday.
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Now that start appears in jeopardy.
"He's a little sore ... it just sort of popped up," Black said.
Latos pitched against the White Sox on Monday and allowed three runs on eight hits in four innings. He complained of a sore shoulder two days later, and his normal side session was canceled.
There's no timetable yet on when Latos will throw again, either on the side or in a game.
"You can't fast forward time, you've got to take your time and worry about what's going on right now," Latos said. "We're not looking forward as far as that [Opening Day] goes now."
Latos, who won 14 games a year ago in his first full Major League season, has allowed 10 earned runs in 10 innings over four Cactus League starts. He also allowed five runs over 3 2/3 innings against Minor League hitters on March 16.
There were certainly no signs of Latos being hurt after Monday's outing.
"Monday, I felt the best I've felt all spring," Latos said.
"I have no idea, it's weird ... bewilderment is more of a word. It felt stiff [Wednesday]. It was a pain where it felt weak to lift my arm."
While other managers have named their Opening Day starters -- and, in many cases, their entire rotations -- Black has steered clear of doing so because of minor injuries to rotation candidates, the latest being Latos.
Starting pitchers Clayton Richard (sore left shoulder) and Tim Stauffer (hip flexor) have worked though minor injury issues in recent weeks. Both are healthy. Richard is to start Sunday in a game against the Angels in Anaheim while Stauffer is scheduled to go Monday against the Brewers.