Mets first baseman Lucas Duda was not in the starting lineup Thursday for the third straight game because of back pain.

"There's a concern," manager Terry Collins said. "It's Defcon 5."

Collins was asked if Duda, who leads the team with 21 home runs and 55 runs batted in, could be headed to the disabled list.

"Today I would have to say probably not," Collins said. "We hope with the medicine [he was given Wednesday] he's much better tomorrow. But I just talked to him a little bit ago. I said `Listen, today we'll give you another day. I need you for this weekend.' If tomorrow it's not much better, we got to start thinking how we are going to make sure we stay healthy as a whole team 'cause to play [undermanned] is sort of tough to do it when you're fighting for the pennant."

Collins added that the "trainers and doctors feel in another 24 hours they'll have a better determination of if it's going to work, how's he's going to feel. The one thing I'm not going to do is aggravate it to the point where it bothers his swing."

Duda hit nine home runs in eight games from July 25 to Aug. 2, but went homer-less in the next seven games before sitting out with the back issue.

advertisement | advertise on newsday

Duda, who was not available before the noon game against the Rockies, had said his back was bothering him a few days before asking out of the lineup.

"He didn't do it by one swing," Collins said. "I'm sure he's talking seven million hits in the last month. It takes a toll."