The Red Sox have lefty pitching prospect Brian Johnson, Brian MacPherson of the Providence Journal reports (Twitter links). Johnson’s role this weekend is uncertain, MacPherson writes, although he’s likely to join the Red Sox’ rotation after the All-Star break. Eduardo Rodriguez and Wade Miley are scheduled to start Saturday and Sunday, respectively. Clay Buchholz left last night’s start with an elbow injury. Whether or not Buchholz needs to be placed on the disabled list, Johnson appears to be a reasonable choice to try to stabilize a shaky Sox rotation.

Baseball America ranked Johnson the No. 82 prospect in baseball heading into the season. MLB.com, meanwhile, currently ranks Johnson the No. 90 prospect in the game, noting that Johnson throws 88-94 MPH but with good sinking action, strong secondary pitches and a good feel for pitching.

Johnson, 24, excelled at Double-A Portland last season and has continued to make progress this year at Triple-A Pawtucket, posting a 2.73 ERA, 8.5 K/9 and 2.7 BB/9 in 85 2/3 innings. He was the No. 31 overall pick in the draft out of the University of Florida in 2012.