Johnson will be recalled to start Saturday's game against the Mariners, Evan Drellich of CSNNE reports.
Hector Velazquez's demotion to Triple-A Pawtucket left a vacancy in the Red Sox rotation for Saturday, so the club will call on one of its top pitching prospects to face the Mariners. Johnson, a lefty, was touched up for four earned runs over 5.0 innings in his lone start for the Red Sox this season. He'll be facing a Seattle team that ranks third-to-last in baseball in terms of wOBA against southpaws.