Matsuzaka had an MRI in New York, which revealed inflammation of the elbow.
Manager Terry Collins told the media that the he did not expect Matsuzaka to return immediately once the 15 days ended, according to ESPN's Adam Rubin.
The 33-year-old is 3-3 with a 3.87 ERA in 28 games (nine starts) this season. He is 56-43 with a 4.46 ERA in his career — six seasons with the Red Sox and two with the Mets.
The Mets recalled right-handed reliever Buddy Carlyle from Triple-A Las Vegas to fill Matsuzaka's spot in the bullpen.
- Chris Mascaro