The All-Star center fielder has an aching bone bruise on his right knee, the same injury that sidelined him for a couple of games in late May. An MRI exam Monday showed the bruise has gotten worse -- Beltran said the doctor told him it just about doubled in size from last month.
Beltran could be out longer than 15 days, too. Asked if the Mets might wait until after the All-Star break to activate him, general manager Omar Minaya said: "That's something that we have to consider."
"It's difficult because of the situation where we are. I think right now basically David Wright is the only guy that is out there playing every day," Beltran said. "But at the same time I'm happy that I know what I have and I know that I don't have to go through surgery. I know that with rest I'll be back."
Fielding a makeshift lineup, the Mets beat St. Louis 6-4 Monday night to move within 1½ games of the first-place Phillies in the NL East -- thanks in large part to Philadelphia's recent slump. It was only the fourth victory in 12 games for New York (35-33).
"We have to believe. We have to be optimistic that we can stay competitive," manager Jerry Manuel said. "We have to guard against that particular mind-set that might permeate in the clubhouse that, man, there's not much left. 'What's going on? I don't know if we can we handle it or we can survive this or not.'"
The 20-year-old outfielder had just been optioned back to Buffalo on Friday after an 18-game stint in the big leagues. He batted .194 with five doubles and five RBIs.
Manuel said the team will take a look at Martinez in center field.
In addition, the Mets made a flurry of roster moves designed to aid their overworked bullpen. They called up right-hander Elmer Dessens and lefty Pat Misch from Buffalo, optioned 40-year-old reliever Ken Takahashi to the Bisons and designated reserve infielder Wilson Valdez for assignment.
New York got good news about starting pitcher John Maine, on the disabled list with weakness in his right shoulder. Maine allowed one run and two hits in four innings of a rehab start for Class-A St. Lucie against Charlotte. He could be back with the Mets by the weekend.
"I just want to get back up there and contribute," Maine said. "I will throw my bullpen in two days and we will go from there. I feel good. I feel like I am ready to go, but the decision is out of my hands."
Fellow starter Oliver Perez, on the DL with right knee tendinitis, started the second game of the doubleheader for St. Lucie. He gave up six runs -- two earned -- and seven hits in three innings, throwing 40 of 56 pitches for strikes.
"Probably the most optimistic point we can take is that our pitching is getting better, from a health standpoint," Manuel said. "And I still believe if you've got good pitching, you've got a shot."
Beltran, however, will be out for a while.
"It's obviously a challenge for us," Wright said. "There's more of an emphasis now on doing the small things right, really trying to play mistake-free baseball. Because we don't have the luxury of playing sloppy baseball and winning a lot of games."
A Gold Glove center fielder, Beltran had been playing through pain and hobbling on the bases for some time. He is hitting .336 with eight homers, 20 doubles, 40 RBIs and 11 stolen bases.
"Yesterday, I couldn't go any more," he said. "The pain that I was feeling the last couple days, it wasn't fun. It's no fun to play like that."
Beltran missed two games in late May because of his sore knee and had a cortisone shot. He did not have another cortisone shot Monday. Instead, threatment will include rest and orthotics, Minaya said.
"The cortisone shot, what it did was basically block the pain -- but the damage was there," Beltran said.
Beltran also started platelet-rich plasma therapy, in which blood is removed, platelets are separated in a centrifuge and then re-injected. Reyes has received the same sort of treatment.
"It was painful," Beltran said.