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Jose Reyes didn’t play in the Mets’ 5-4 loss to the Cardinals Wednesday night because of the left rib cage injury he suffered during the first game of Tuesday’s doubleheader — and Terry Collins sounded pessimistic about Reyes playing Thursday.

“My guess is we’ll be very careful [Thursday], even if he’s OK,” the manager said of the day game.

The Mets are trying to avoid a lengthy absence for Reyes, who felt the muscle pull when he grounded back to the pitcher in the sixth inning. He remained in the game and the injury worsened when he was up in the eighth.

“We’re gonna take it day-by-day and see what happens,” said Reyes, who received a cortisone shot on Tuesday and ice treatment Wednesday.

Wilmer Flores started at third in Reyes’ place in Tuesday’s nightcap and again on Wednesday. He made the most of the opportunity Tuesday, with three hits, but he is still trying to perform consistently against righties, going 1-for-4 against the Cardinals’ Adam Wainwright and Jonathan Broxton.

Collins said he has been impressed with how Flores is hitting to right-center lately.

Collins gave Neil Walker a bit of a vote of confidence before the game despite the second baseman’s lack of production and Walker repaid the manager by getting on base four times and driving in a run.

Walker didn’t play Sunday. Monday’s game was postponed and he sat the first game of Tuesday’s doubleheader before returning for the nightcap, when he went 0-for-3 to extend his hitless streak to 13 at-bats.

“Sometimes in this game, you’ve got to take a couple steps back and slow things down and get back to square one,’’ Walker said. “A lot of times, when things aren’t going the way you want them to go, you tend to press and I think I was doing that for a little bit.”

If his struggles persist, Collins could be forced to make changes to the lineup, perhaps with Flores or prospect Dilson Herrera.