According to multiple news outlets, Rodriguez was put on a stretcher and escorted out of the stadium after collapsing about a half-hour after the game's final pitch. About 10 minutes earlier, he had requested to conduct an interview sitting down because it pained him to stand.
Mets spokesman Jay Horwitz told The Associated Press that Rodriguez went to the hospital by ambulance, but said it was only to avoid traffic.
Rodriguez had fallen victim to a similar series of spasms about an hour before the game. With a group of teammates huddled around him, he endured a series of spasms that left him barely able to walk -- and certainly unable to pitch.
"I've never experienced some pain like the way that I have right now," Rodriguez said after the game. "The pain is strong, even to walk."
Running in the outfield during batting practice, Rodriguez began to feel tightness in his back and returned to the clubhouse for treatment. Within moments, however, the pain had increased. Despite taking muscle relaxants and other treatments, he lay immobile on a training table for about an hour.
"It came out of nowhere," he said.
Setup man J.J. Putz, who had fought his own battle against neck stiffness in recent days, took Rodriguez's place in the ninth inning on Saturday.
"He was in a tough position before the game," manager Jerry Manuel said of Rodriguez. "He couldn't walk. He was in bad shape."
Rodriguez said that it is the first time he has been affected by back spasms -- and that gives the Mets hope that he may recover quickly. But they cannot be certain until they re-evaluate him on Sunday.
It's just the latest setback for the Mets, who in recent days have endured injuries of varying severity to Carlos Delgado, Jose Reyes, Carlos Beltran and Ryan Church. In Saturday's game, only two regulars -- David Wright and Luis Castillo -- played at their Opening Day positions.
Rodriguez, who signed a three-year, $37 million deal to join the Mets this past winter, is 12-for-12 in save situations with a 0.87 ERA.
Anthony DiComo is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.