Two X-rays taken on Johnson's finger showed no damage, but a more extensive examination by team physician Tom Mehlhoff revealed a small microfracture. Johnson has missed two games and is expected to be sidelined no less than a week, but no more than two weeks.
The 24-year-old Johnson had played in only three games at the time of the injury. He was hitless in seven at-bats.
In other Minor League happenings, right-hander Jose Capellan seems to have run into some troubles on the mound since he was cut on the final day of Spring Training. Though he had a nice spring showing and was in the running for the fifth-starter job until the very end, Capellan is winless in three starts for Round Rock and has allowed 19 earned runs over 14 innings for a 12.21 ERA.
Bud Norris, one of the club's top pitching prospects, is the lone starter having any success for the Express so far this season. He's 0-1 with a 2.16 ERA over three starts, having allowed seven runs (four earned) over 16 2/3 innings with nine walks and 18 strikeouts.
In Double-A Round Rock, Brad James and Sergio Perez, two pitchers who spent part of Spring Training with the big league club, have fared well. James is 1-0 with a 2.81 ERA over three starts, and Perez is 2-0 with a 3.60 ERA over three starts.
The strikeout-to-walk ratios for the two are a bit bothersome, however -- James has walked 11 and struck out seven, while Perez has walked eight and struck out three.
Catcher Koby Clemens was called up to Corpus Christi on Saturday after hitting .227 in 13 games for Class A Lancaster.
Clemens had one homer and eight RBIs for the Jethawks, and six of those RBIs came on Friday in an 11-8 win over Rancho Cucamonga. Clemens won the game with a three-run walk-off homer.
Clemens fills the roster vacancy created by catcher Brian Esposito's callup to Triple-A. Esposito was summoned to Round Rock after J.R. Towles was called up by the Astros to replace the injured Humberto Quintero.
Alyson Footer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.