The superstar shortstop played a rehab game for Class-A Brooklyn Monday; he doubled and played six innings.
Manager Terry Collins said Reyes will be activated Tuesday in time for the opener of a three-game series against St. Louis.
Leading the majors with a .354 batting average and 15 triples, Reyes has been sidelined since July 3 with a strained left hamstring. He was eligible to come off the disabled list Monday, but the Mets wanted him to test his leg in a game first.
Reyes went 1 for 3 and scored a run in Brooklyn's 11-5 loss to Lowell.
All-Star right fielder Carlos Beltrán missed his third straight game with a bad case of the flu. Collins said Beltrán was headed to the doctor for tests and needed one more day of rest.
"He did say he felt better yesterday, but we got some news today that he's still a little bit under the weather," Collins said, adding that Beltrán had lost a lot of weight. "He's got a good case of it. I hope it doesn't spread. You know how it can go around the clubhouse."
Collins said Beltrán was available as a pinch-hitter in Monday night's 4-1 loss to Florida and would have batted in the ninth inning if one more batter had reached base.
Scott Hairston replaced Beltrán in right but left the game after two innings. Batting cleanup, Hairston fouled a ball off his left shin in the first inning and jogged gingerly down to first base on a groundout.
The Mets said Hairston has a bruised left shin. X-rays were negative and he is day to day.
Hairston filled in for Beltrán on Saturday and had a huge game, hitting a long homer and driving in a career-best five runs during an 11-2 victory over Philadelphia.
Elsewhere, third baseman David Wright (back) went 3 for 6 with three runs scored in his fourth rehab game for Class-A St. Lucie. He played nine innings at third and the target for his return is this weekend at Florida.
Based on reporting by The Associated Press.