He waited until after the club's game Sunday vs. the Braves to see how his bullpen was used before tabbing Wade Miley for the spot start.
Gibson could've brought up a prospect to fill in for Daniel Hudson, who went on the disabled list on Saturday with a right shoulder impingement, but instead opted for a more battle-tested arm.
Miley began the season in the bullpen as the D-backs' long relief option, but in seven starts last year, he was 4-2 with a 4.15 ERA.
In 8 2/3 innings of relief this season, Miley has allowed three earned runs on seven hits.
"He's been in the Major Leagues and he's as equipped as anybody," Gibson said. "I just felt he'd thrown the ball good and he's done a good job. He should have some length for us, five or six innings would be great. If it doesn't happen, we'll adjust."
Gibson said D-backs reliever Jonathan Albaladejo, whom the club promoted from Triple-A Reno on Saturday with Hudson's trip to the DL, would likely come out of the bullpen if Miley struggles.
The D-backs will wait until after Monday to determine whether Miley will stick in the rotation while Hudson is sidelined or look to the Minor Leagues for another replacement.
"As it's going right now, it's a day-to-day thing," Gibson said. "We'll see how he throws tonight and we'll make a decision from there."