The club already was in limbo for Saturday night, as Brandon Beachy had been demoted, and Sunday, the normal day for Brett Anderson, who left his Tuesday start in the third inning with left Achilles irritation.
Prospect Zach Lee had been positioned to make his Major League debut Saturday night in place of Beachy, although the club never made that official. Dodgers manager Don Mattingly said Greinke would be placed on paternity leave and a pitcher would be called up, but wouldn't say who.
After Thursday night's game -- a 3-0 win for the Dodgers and Clayton Kershaw -- the club announced that Thomas would start Friday. It will be the first Major League start for Thomas, who has a 5.23 ERA in seven relief appearances this season.
Greinke, who has a scoreless-innings streak of 43 2/3 and a 1.30 ERA, was originally scheduled to start Friday night. Mattingly said he was hopeful Greinke could rejoin the club in time to start Saturday night but said a return in time for Friday night's game was "unrealistic."
Mattingly also said he was hopeful Anderson could make his start Sunday after successfully testing the injury Thursday with agility drills, throwing, and pushing off the bullpen mound without throwing.
Anderson, who still wears a protective boot when not at the ballpark -- "In case I trip on a curb or get hit by a cab" -- said his workout Thursday was a "good step" and he had "no issues."
He will throw a bullpen session Friday, possibly with some fielding practice, as he suffered the injury fielding a batted ball. He said he wouldn't need to be disabled, barring a setback.
Mattingly, who said he received a call from Greinke at 5 a.m. Thursday with the news he was leaving, downplayed the severity of the situation.
"We're OK," he said. "It's not like he's out for the season."
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.