"It's a little sore," Upton said. "It snuck up on me. Most of the time you have time to break it down … but I didn't."
San Diego interim manager Pat Murphy said Upton "bruised his thumb pretty bad." Murphy said the team will keep an eye on Upton. He hopes this isn't more than a day-to-day thing.
"If he's down for anything longer than a day, we'll be concerned," Murphy said.
There's about three feet of padding that goes up from the ground down the third-base line, but nothing above that other than the rails that separate the fans from the field. That's where he hurt his thumb.
"There isn't a better spot for padding [than] there. That railing is pretty inconvenient," Upton said.
Upton had a double in four at-bats on Monday and was replaced by pinch-hitter Clint Barmes in the eighth inning as shortstop Alexi Amarista moved to left field.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.