With an impressive spring, either Mikolas or Tolleson could earn one of the Rangers' final bullpen spots.
In other injury news, center fielder Leonys Martin remains day to day with back soreness, and left-hander Rafael Perez is slated to throw live batting practice Saturday after missing a few days with a right hamstring strain.
Perez, who last pitched in the Majors for the Indians in 2012, signed a Minor League deal with a Spring Training invite in January.
AJ Cassavell is a reporter for MLB.com. Follow him on Twitter @ajcassavell. This story was not subject to the approval of Major League Baseball or its clubs.