HOUSTON -- Conor Jackson was out of the starting lineup on Sunday as D-backs manager Bob Melvin decided it was time for his left fielder to get a rest.

"I can't remember his last off-day," Melvin said.

That's because the last time Jackson didn't start a game was June 27 when he came in as a pinch-hitter. The last time he got a complete day off? June 6.

Despite the heavy workload, Jackson said physically he is not tired, thanks no doubt to a the rigorous training regimen he put himself through during the offseason.

"I think he came to Spring Training with a different look and he really wanted to establish himself this year as a good Major League player and he's certainly done that," Melvin said. "It's a day-to-day proposition for him. He doesn't take anything for granted. He's had that look in his eye since the first day of Spring Training."

"Physically, I'm fine," Jackson said.

It's been a struggle for him at the plate lately, though. Over the last week, he is just 4-for-30 (.133) and does not have an extra-base hit.

"It's more of a mental thing," Jackson said. "I'm just pressing a little bit. I feel like I've been hitting some balls hard, but I think it's more of a mental thing."

Monday is a scheduled off-day for the D-backs so essentially, Jackson will get two days off to clear his head.

"Melvin is a good judge when it comes to that stuff," Jackson said. "So I trust his opinion and trust his judgment on this."