GLENDALE, Ariz. -- Dodgers manager Don Mattingly reluctantly conceded Monday that injured pitcher Zack Greinke won't have a sufficient foundation of pitches to start in Australia later this month.

Greinke played catch Monday and reported improvement in his strained right calf, but Mattingly said Greinke's return to a mound remains unknown.

"From a standpoint of having 90 pitches, he won't be there," Mattingly said.

Greinke was injured four pitches into his first start on Thursday. The Dodgers leave for Australia on March 16, and Mattingly said Greinke needs to throw a bullpen session before he returns to game action, and he needs to have his arm strength built up to throw 90 pitches in order to start a regular-season game.

The Dodgers will choose two starters from Clayton Kershaw, Hyun-Jin Ryu and Dan Haren for the Opening Series against Arizona.