Webb is 4-0 with a 1.39 ERA, nine holds and two saves in 36 relief appearances with Atlanta. The move was retroactive to Saturday.
Webb experienced discomfort after pitching one-third of an inning Friday, his only outing since the All-Star break.
“He felt it after that first outing,” Braves manager Brian Snitker said. “He only threw five pitches, I think, but still, he woke up and it was tight. It was good. I’m glad he didn’t try to pitch through it and something happens.”
It is not known how long Webb will be sidelined.
Webb, 25, was called up from Gwinnett on April 14 and made his Major League debut on April 16 and recorded his save on April 29 against the Padres.
Ynoa, 21, made his big league debut earlier this season, pitching two scoreless innings of relief in his only appearance on June 16.
“He’s got a big arm,” Snitker said. “He’s another young guy. I think when he gets his command, he has the pitches. What I saw the two-inning stint that he had here, it was very impressive. His last couple outings in Triple-A have been really good.
“He’s a young guy we’ve just got to keep pitching. His upside is huge with that arm.”
The hard-throwing Ynoa opened the season at Class A Advanced Florida, going 0-1 with a 3.27 ERA in three starts. Ynoa moved up to Double-A Mississippi on April 19 and then advanced to Gwinnett in mid-May.
Ynoa was 1-2 with a 5.27 ERA in six relief outings with Mississippi, and then he was 2-2 with a 5.20 ERA in nine games (seven starts) with Gwinnett, where he struck out 39 and walked 19 over 36 1/3 innings. Overall, he has struck out 70 in 61 innings in the Minors this season.