Mets manager Terry Collins said surgery had not been mentioned as an option, and the team would not be able to see if there was structural damage until the inflammation is reduced.
"He's not going to be back in 15 days. He needs to rest the elbow up," Collins said. "The inflammation needs to really subside to get a better idea of what's going on. It'll be at least seven to 10 days without him throwing and then we'll have more to say after that."
Matsuzaka had been bumped to the bullpen on July 20 after a month and a half of being mainly a starter. He carried a 2-3 record and 4.24 ERA as a starter but has had more success in relief, striking out more than 10 batters per nine innings and holding a 3.25 ERA.
Matsuzaka has pitched 74 1/3 innings in 2014.
"There's only one way to get hurt and that's pitching. I'm sure it's just from all the innings," Collins said. "You pile up all those innings and throw all those pitches, there's going to be damage. Can't help it. I'm sure that's how it is, and I hope it's not that severe where, with rest and rehab, it'll be fine."
The injury hampers the Mets' bullpen because Matsuzaka had the versatility to make a spot start. Collins said that Carlos Torres would now fill that role, and if someone was needed for more than one start, the team would have to call someone up.
Carlyle has pitched in five games for the Mets this year, allowing one earned run over seven innings. He has a 2.16 ERA in 30 appearances in Triple-A.
• Collins said that Juan Lagares, who was out of the starting lineup on Saturday, would get some work done in the batting cages. Lagaras has gone 3-for-28 with no extra-base hits since the All-Star break.
"I thought a day might relax him a little bit," Collins said. "Right now, he's trying way too hard. We're trying to reduce the strike zone and he's enlarging it."
• Collins said one of the reasons for starting Eric Young Jr. on Saturday was that Brewers starter Wily Peralta has been prone to opponents stealing bases.
"If Eric gets on, [Peralta] doesn't hold them on very good," Collins said. "If he gets on, he can score. The last two games he's played in, we've won, and he's had something to do with it."