Mets manager Terry Collins said Friday that the 33-year-old Matsuzaka felt something in his elbow a day earlier.
Matsuzaka pitched two innings and gave up three earned runs in the Mets' 9-1 loss at Milwaukee on Thursday night.
''He said when he was loosening up, he could feel it a little bit, thought it was nothing that he couldn't pitch through, but when the game was over it bothered him pretty good,'' Collins said before Friday night's game against the Brewers.
Matsuzaka is 3-3 with a 3.87 ERA in 28 games this season. He's made nine starts.