General manager Sandy Alderson said Davis would be dispatched to New York on Sunday and would undergo an MRI after the Labor Day weekend.
"It's horrible," Davis said. "I just started playing a little better and started to feel confident again and stuff like that. It sucks, because I don't know if I can get back to play in any games this year. But at least I was starting to play better. Stuff like this happens."
Manager Terry Collins said Lucas Duda primarily will play first base, with Josh Satin facing left-handed pitching. Rookie Wilmer Flores, now playing third base, could see limited action at first base once David Wright returns from the disabled list.
Davis clutched his right side after making contact with a third-inning pitch from Washington Nationals right-hander Dan Haren and departed the game. He said he had been dealing with a tight and sore oblique for a couple of months and had been waiting for it to give, but actually thought he was in the clear because the issue stopped nagging him a week ago.
"Just standing straight up it's not bad," Davis said. "I was eating some seeds on the bench and I coughed and it felt like someone stabbed me, so I don't think that's a good sign. But who knows?"
Because side-muscle injuries typically take several weeks to heal, Davis likely will be unable to return this season. The Mets have only 28 games remaining. And that raises questions about whether the 2008 first-round pick's career is through with the Mets.
Davis is hitting only .205 with nine homers and 33 RBIs this season and spent nearly a month at Triple-A Las Vegas this summer.
Davis, again eligible for arbitration this offseason, is making $3.125 million in 2013. While not a clear-cut non-tender candidate, a trade or cutting him loose in December undoubtedly will have to be internally debated by team officials.
"You have to take into account the entire body of work, as abridged as it might be," Alderson said. "It's what we have available to us, and it's what we'll use to evaluate him and where we are going into next season."
"I can't control any of that," Davis said about his future with the organization. "All I can control is to try to get healthy."
The Mets non-tendered another former first-round pick, Mike Pelfrey, last December.
Davis is hitting .267 with four homers and 17 RBIs in 48 games (38 starts) since rejoining the Mets from the minors.
"Hopefully I can do it for two half-seasons next year," Davis said.
Added Collins: "I feel terrible for Ike. He went to the minor leagues. He worked on some things -- very hard on some things. He came back and you started to see some signs; 2013 is going to go down as a real frustrating year for Ike Davis."