PHOENIX -- With Justin Upton out of the lineup with a bruised left thumb, D-backs manager Kirk Gibson has been deciding on a game-by-game basis who should start in right field.

On Wednesday, Gibson played Jason Kubel in right and Gerardo Parra in left.

On Thursday, Gibson switched Kubel and Parra.

Parra, who won a Gold Glove Award last year, is regarded as the better defender of the two.

"[The Braves] have a lot of left-handed hitters in there today and [Josh] Collmenter is on the mound," Gibson said when asked what led to his decision to flip the outfielders. "I just thought I'd rather have Parra in right tonight -- they'll probably hit them all to left for all I know. It's just the thought process; if they hit the ball in a corner that way, Parra has a stronger arm to maybe cut down a triple."

Kubel said he doesn't really have a preference, but allowed that he was "a tad" more comfortable in left than he is in right.

Upton expects to return to lineup soon

PHOENIX -- D-backs outfielder Justin Upton was out of the lineup for the third straight game on Thursday, but he seems to be getting closer to returning.

Upton jammed his left thumb while sliding into second base in the first series of the season against the Giants, and it has bothered him since.

"Every morning when I get up it's a little better, which is a positive sign," Upton said. "I don't want to re-irritate it and have it come back. The good thing is that it's getting better every day, so we'll see how it is tomorrow."

With fellow outfielder Chris Young out with a shoulder injury, the D-backs could certainly use Upton's bat in the lineup.

"To be honest with you, I feel like I'm close," Upton said.

Initially, Upton tried to play through the pain, but it clearly was taking a toll on his performance.

In his first 40 plate appearances this year, Upton hit .212 with two doubles and no homers or RBIs.

"It's not fun, and I think it got to the point where I wasn't helping anybody," Upton said. "I wasn't helping the team, so I figured if I could get it right, that's better for me and the team."

Torn oblique is the latest injury for Blum

PHOENIX -- D-backs infielder Geoff Blum's latest injury is no laughing matter, which is a good thing considering his injured left oblique hurts when he laughs.

Blum injured the oblique while swinging a bat on Tuesday night during batting practice and was placed on the 15-day disabled list.

"Just last swing of my third round of BP the other day," Blum said. "I felt it pop and tear, and sure enough tore it. Never, this is the first time I've had that injury. Hurts like [heck]."

Blum spent most of the 2011 season on the disabled list due to a right knee injury and a fractured right pinkie finger. The two injuries cost him 127 games last year.

"They said it was a pretty good tear or strain or whatever you want to call it, and we're just going to play it day by day," Blum said. "Obviously, [I'm out] 15 days, but I've heard anywhere from four to eight weeks, so it just depends on how I respond to the treatment."

The injury just adds to the frustration Blum has felt since signing a two-year deal with the D-backs prior to last season.

"The only person I can be mad with is myself, but it's just one of those freak things," Blum said of the injury. "It has nothing to do with how I train or what I eat or drink, it's just one of those things that happens in baseball."

And it's happened too often lately for Blum's liking.