Johnson, 29, has been pitching well at Rochester this season, posting an 8-4 records and 2.75 ERA with 83 strikeouts and 38 walks in 98 1/3 innings over 16 starts. His last start came Sunday, when he gave up one run on two hits over seven innings, so he'll be on normal rest Friday.
The lefty also made one spot start with the Twins on May 1 in the second game of a doubleheader against the Dodgers. He tossed 4 1/3 scoreless innings, but couldn't go through the fifth, as he threw 106 pitches.
"He's been throwing great like a lot of guys down there," Gardenhire said. 'I know last time he was up here his pitch count got high, but he has good stuff. He's been pitching well. That's who they recommended and he's in line, so I'm happy with it."
The Twins are likely to option right-hander Yohan Pino to Rochester after he starts Thursday against the Mariners to make room for Johnson. Pino wouldn't have to miss a start with the Twins because of the four-day All-Star break that begins Monday.
Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.