De Vries attempted to throw a bullpen session before Friday's game against the Orioles, but he still felt tightness in his forearm. De Vries last pitched on March 29 in Spring Training, but he exited that start after three innings because of discomfort in his forearm.
"He felt it with his curveball," general manager Terry Ryan said about De Vries' bullpen session. "If he doesn't feel right, he can't go out there. It's as simple as that."
De Vries, who posted a 4.11 ERA in 17 outings with the Twins last year, is eligible to come off the DL on April 14. He said he'll have an MRI exam on his forearm in Minnesota on Monday and is hopeful it's nothing serious.
"It's pretty disappointing," De Vries said. "My [bullpen session] was going great, but then I started throwing some offspeed pitches with my curveball and slider and [the tightness] just came back."
Hernandez will be making his Twins debut, as he was acquired before last year's Trade Deadline in the deal that sent Francisco Liriano to the White Sox. Hernandez was scheduled to start for Triple-A Rochester on Sunday, so he'll be pitching on normal rest.
Hernandez made one spot start for the White Sox last year, allowing eight runs in four innings against the Red Sox on July 18. He had a combined 3.32 ERA in the Minors last season and impressed this spring by throwing 11 scoreless innings in Grapefruit League play.
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.