PITTSBURGH -- Jordan Lyles ' encore to his near-perfect game will come one day earlier than originally planned.

Lyles, who carried a perfect game one out into the eighth inning against the Rockies on Tuesday, is scheduled to start Sunday against the Pirates. It's the spot that would've been occupied by left-hander Joey Lucchesi, but Lucchesi was placed on the disabled list Tuesday.

In two starts this season, Lyles has struck out 16 and allowed one earned run over 12 1/3 innings. He owns a 2.53 ERA this year in 15 appearances, the first 13 of which came out of the 'pen.

Because of Wednesday's off-day, Lyles is still ticketed to start on normal rest. But the Padres do not have a starter lined up for Monday.

"Everything is probably predicated on what happens in our bullpen over the next few days," manager Andy Green said. "We'll make decisions that are best for us to win today's game, and we'll make our rotation decision after that."

Robbie Erlin and Bryan Mitchell are the most likely candidates to fill that void. With rain in the forecast over the next two days in Pittsburgh, the weather could shake things up further.

Munoz to begin throwing program

Hard-throwing righty prospect Andres Munoz is slated to throw off a mound Monday, the first time he'll do so since he sustained a UCL sprain in his throwing elbow in April. Munoz is one of the club's top bullpen prospects and is ranked No. 20 on the overall organizational list by MLB Pipeline.

Munoz burst onto the scene in the Arizona Fall League last year, posting a 1.04 ERA and a 0.69 WHIP in nine appearances. The 19-year-old turned heads with a high-octane fastball that routinely touched triple digits. MLB Pipeline graded the pitch as an 80 -- the highest possible score on the 20-80 scale.

There's plenty of development ahead for Munoz, and he will need to lower his walk rate significantly. But the Padres feel he has closer potential. If his rehab goes according to plan, he'll begin the season at Class A Fort Wayne or Class A Advanced Lake Elsinore.

Padres officially release Headley

Chase Headley has hit the open market.

The Padres officially released the veteran third baseman Friday, having designated him for assignment last weekend. Headley was batting just .115/.233/.135 in 60 plate appearances this year.

San Diego is on the hook for the remainder of Headley's 2018 salary. If he's picked up by another team, it will owe Headley a pro-rated version of the league minimum.

Headley, owed $13 million in 2018, arrived in San Diego along with Mitchell in a December trade with the Yankees. The Padres took on his burdensome contract mostly so they could acquire Mitchell, whom they believed could be a serviceable rotation piece. Mitchell has since struggled and was demoted to the bullpen earlier this month.

As for Headley, it's unclear what's next. He's in the 12th season of a big league career in which he owns a .263/.342/.399 slash line. He was a productive piece on a postseason team as recently as last year with the Yankees. But his start to the 2018 campaign has raised serious questions about whether the 34-year-old third baseman can turn things around.

"He experienced no luck with us in 60 at-bats, and that's a very short sample to make an ultimate judgement of a guy's worth when he's played over a decade of quality baseball," said Green. "If he gets that opportunity and feels good about it, I think he'll take it. There's good things out in front of him."

AJ Cassavell covers the Padres for MLB.com. Follow him on Twitter @ajcassavell.