Fife, on the 15-day disabled list since July 7 with right shoulder bursitis, had been scheduled to make a rehab start for Triple-A Albuquerque.
The club hasn't yet announced the plan. Manager Don Mattingly was non-committal on Friday, saying Fife will pitch on Sunday for the Isotopes or the Dodgers, but he wouldn't elaborate.
By inserting Fife, the Dodgers will give their five-man rotation an extra day of rest. The juggling also shifts Greinke from facing the fourth-place Cubs to the second-place Cardinals.
It's unclear how the Dodgers will make room for Fife on the 25-man roster. Rookie right-hander Chris Withrow could be optioned, although he recently has been used in more important situations.
A more likely alternative is reliever Carlos Marmol, especially since the signing of Brian Wilson, another former All-Star closer. Marmol hasn't pitched in a week and wasn't sharp in his first two Dodgers appearances.
The former Cubs closer pitched for the first time as a visitor at Wrigley Field in Friday's 6-2 win over Chicago, working around a walk and a single for a scoreless ninth.
Also unclear is what will happen on the next rotation cycle -- whether Fife will remain in the rotation and displace Chris Capuano, or if Fife will be optioned back to Albuquerque.
Fife is 3-3 with a 2.76 ERA in eight starts for the Dodgers this season.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.