"It was just a little tweak," Upton said. "It wasn't anything serious, but it stiffened up on me a little bit once I got settled in the dugout. That's why I came out of the game."
D-backs manager A.J. Hinch said he may keep Upton out of the lineup again Tuesday, when the team opens a six-game homestand.
"He's truly day to day," Hinch said. "As of now, I think we've avoided a little scare."
Upton, who was named the National League's Player of the Month in May, did not seem to think that the injury was serious.
"I feel better today," he said before Monday night's game with the Padres. "A little soreness, but that is expected. I guess we'll see after tomorrow."
Upton said he would probably be examined by team physician Michael Lee when the team gets back to Phoenix.
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.