CLEARWATER, Fla. — The Phillies lost their second pitcher in five days as they learned Tuesday that Mark Leiter Jr. will be sidelined until late April or early May because of a mild flexor strain he suffered during his previous outing.

Leiter will open the season on the disabled list with Jerad Eickhoff, who is expected to be out until early May with a strained back muscle. Leiter was expected to be one of the team's eight relief pitchers, working as a long reliever. That role will likely be filled by Drew Hutchison or Jake Thompson, who is transitioning this spring to the bullpen. Hutchison would first have to be added to the 40-man roster.

"We have a group of guys who have shown well in spring training and are really pushing towards that finish line," manager Gabe Kapler said.

Leiter allowed two runs in his first four outings this spring before allowing four runs March 16 in an outing that ended with his getting injured. Another candidate to take his place is Ben Lively, who would enter the mix if he is not named the team's fifth starter. Lively allowed three hits in five shutout innings Tuesday. The Phillies have challenged him this spring to not pitch to contact. He did a good job Tuesday, as he established his four-seam fastball and racked up four strikeouts. The final rotation spot seems to be coming down to Lively and Zach Eflin. Lively has never pitched out of the bullpen, but said he is not opposed to trying it if it gets him a roster spot.

"I'll pitch anywhere," Lively said. "I don't care."

Extra bases

Jake Arrieta threw a bullpen session Tuesday morning and is on track to make his spring training debut Thursday against Detroit in Clearwater. … Pedro Florimon made a series of nice plays at third base and remains in the mix for the final bench spot. He has a hit in his previous four games. …The Phillies sent catcher Logan Moore, outfielder Andrew Pullin, and infielder Mitch Walding to minor-league camp. … Vince Velasquez will start Wednesday in a minor league game. Nick Pivetta will start against Toronto in Dunedin.