After playing in the outfield for the first time in his career June 15 against the Angels, Pennington has served as the club's fourth outfielder while Ender Inciarte is on the disabled list with a strained right hamstring.
In Sunday's 6-4 win over the Padres, Pennington made his second start in left field to allow a slumping A.J. Pollock to take a day off, while David Peralta shifted from left to center. Peralta hit a solo homer in the third inning.
"It's not going to be easy for him," D-backs manager Chip Hale said. "He played out there in Anaheim, did a heck of a job, but you can't expect him to be a savvy outfielder. He's just going to give his effort that he always does."
Pennington has been taking fly balls in left field during batting practice and said he feels that has helped him get more acclimated to the new position. The 31-year-old even had an outfield assist in his previous start in left.
But Pennington said his goal is to just be an adequate fill-in, giving an opportunity for one of his teammates to take a day off while the team is low on outfielders.
"I'm just going to try and keep it simple, catch the ones I'm supposed to catch," Pennington said. "Obviously the challenges are the difficult plays, the ones down the line and off the wall and those kind of things. I'm just going to try to position myself the best I can."