The second baseman broke his right leg when he fouled off a pitch in the fourth inning of New York's 4-1 victory over the Los Angeles Dodgers on Friday night.
It was the second time this season Valentin went down with an injury to his right leg. Earlier this year, he partially tore a ligament in his knee.
"It's probably going to take me all the way until September to come back and play," said Valentin, hitting .240 with three homers and 18 RBI in 51 games. "They're going to put a cast on it and I guess I have to be like that for six weeks. Hopefully, the team can play well and give me a shot to be in the playoffs."
Oliver Perez (9-6) allowed a run and six hits over 7 1/3 innings in his second start since coming off the disabled list. It was the 11th time in 17 starts this season that the left-hander allowed fewer than three earned runs. He struck out eight and walked three. In two starts against the Dodgers last season with Pittsburgh, Perez was 0-2 with a 14.04 ERA.
Billy Wagner pitched a perfect ninth for his 21st save in 22 attempts.
Valentin, one of seven former Dodgers on the Mets' 25-man roster, was replaced by Ruben Gotay. Already a pleasant surprise, Gotay figures to get even more playing time at second base now.
"It went numb right away. As soon as I tried to walk back into the batter's box, I felt like something popped," Valentin said. "It's not a complete break, just a little crack. But it's enough to get me out of the game for six weeks. It seems like everything happens in the same leg."
The switch-hitting Valentin was playing in his 29th game after missing 5½ weeks with a partially torn ligament in his right knee, which has been supported by a brace since his return. He had planned to put off surgery on his knee until after the season in part because of a $4.3 million team option for next year that would become guaranteed if he reached 400 plate appearances.
It now appears unlikely he will hit the mark.
"I thought I didn't have as much time as I did and I rushed the throw," Hernandez said. "The ball was wet, I was off-balance and I just threw it in the dirt."
Beltran drove the next pitch to right-center for his 18th homer.
"The ball just stayed up," said Hernandez, pitching in his second game with the Dodgers after getting released by Cleveland. "One thing I've battled all year was command in the strike zone. But one positive I can take from here is that I'm throwing strikes again. I couldn't ask for anything more, especially after being out for a month and not pitching in game situations. Now I've got to work on throwing better strikes."
Brett Tomko, making his second impressive start since replacing injured Randy Wolf in the Dodgers' rotation, allowed an unearned run and five hits over six innings. He struck out three and walked one.
"It feels good to go out there and pitch well. It's definitely better than going out there and struggling out of the 'pen," said Tomko, who recently stated that he would like to be a starter somewhere -- if not with the Dodgers.
Wolf threw off a mound for the first time since going on the DL because of an impingement in his shoulder. He is scheduled to have another bullpen session on Sunday, and barring any setbacks will make a minor league rehab start next Wednesday.
"When Randy comes back, he's going to be in the rotation. It's a tough situation, so I try not to look too far in advance," Tomko said. "In the back of your mind, you wonder where you're going to fit in, but that's really not my decision. If I keep going out and pitching well, I'll put pressure on them to make a decision."
David Wright capitalized on Dodgers center fielder Juan Pierre's fourth error of the season, driving in Anderson with a first-inning single. Anderson reached on a two-base error by Pierre, who called off left fielder Luis Gonzalez at the last instant and then backed off the ball to avoid a collision.
Nomar Garciaparra sent Perez's first pitch of the second inning over the center-field fence to tie the score. It was only the third homer this season for the six-time All-Star.
- Dodgers closer Takashi Saito wasn't able to pitch for the second straight night because of tightness in his right shoulder.
- Dodgers 2B Jeff Kent led off the sixth with his 523rd double, tying Willie Mays for 33rd place.
- Pierre extended his hitting streak to 13 games with a single, then stole second and third later in the first inning.
- Wagner needs 13 strikeouts to bring his career total to 1,000. The only left-handed reliever to reach that plateau is former Mets and Dodgers closer Jesse Orosco.