PITTSBURGH -- The D-backs felt plenty good about beating the Pirates, 4-3, on Wednesday night, but there was also a strong undercurrent of concern in the clubhouse following the game.

That's because All-Star outfielder Justin Upton was forced to leave the game in the ninth inning with a right oblique strain. While the injury certainly seemed like one that would require a stint on the disabled list, both the team and Upton tried to be positive after the game.

"No," Upton said when asked if he was concerned. "I'm trying to be as optimistic as possible. I can't say how I'm going to feel tomorrow. We'll see how I feel today and go from there."

Upton singled with one out in the ninth, and with Mark Reynolds at the plate, he attempted to steal second base. After a step or two, Upton pulled up in obvious pain.

"It makes for a tough night because he's obviously a key part of our lineup and it's tough to see him go down like that," D-backs manager A.J. Hinch said. "And those are tricky injuries where you don't how long they're going to be. We'll know more tomorrow, but it's a tough blow for this team."

Upton is hitting .301 with 22 doubles, six triples, 20 homers and 66 RBIs.

Last season, Upton suffered a strain of his left oblique that put him on the disabled from July 18-Aug. 29.