Mets third baseman Brett Baty reacts after lining out to...

Mets third baseman Brett Baty reacts after lining out to end an MLB game against Atlanta at Citi Field on May 11. Credit: Kathleen Malone-Van Dyke

SAN DIEGO — Brett Baty’s season might be over after he suffered a significant injury with Triple-A Syracuse.

He fractured his left index finger and is expected to miss four to six weeks, the Mets announced Sunday. He got hit by a pitch on a check swing on Thursday.

That is a bad injury with particularly bad timing for Baty, who could have been in line for a return to the majors when rosters expand next Sunday.

“It’s a big blow,” manager Carlos Mendoza said. “Especially where we’re at in the season. His name was one of the names probably in consideration for September. So yeah. Now we gotta get him back healthy, however long that is. It’s a big blow for him and a big blow for us.”

Whether Baty can return at any level, this has been something of a lost season for the 24-year-old. He opened as the Mets’ starting third baseman, batted .229 with a .633 OPS for two months, lost his job to Mark Vientos and was demoted to the minors.

With Syracuse, Baty hit .262 with an .886 OPS and learned to play second base, giving him valuable defensive versatility. But the Mets haven’t had room for him on the major-league roster, in part because Vientos has taken off.

Blackburn sidelined

Paul Blackburn avoided major injury, but he couldn’t avoid the injured list.

The Mets put the righthander on the 15-day IL with a bruise on Sunday, two days after he got hit in his pitching hand by a line drive.

All involved expect Blackburn to be ready to return as soon as he is eligible to do so (Sept. 8), which would mean missing two or three starts.

“He should be ready to go, fully built up,” Mendoza said.

Regarding Blackburn’s replacement, Mendoza said there were “a couple of guys in the mix” but mentioned only one by name: Tylor Megill.

Who else makes sense?

“Megill,” Mendoza said.

Megill has a 5.17 ERA in 10 games with the Mets this year. They demoted him to Triple-A Syracuse upon acquiring Blackburn from the Athletics at the trade deadline.

In four starts back in the minors, Megill has a 4.22 ERA. He most recently tossed 4 2/3 scoreless innings Saturday.

An off day Monday gives the Mets flexibility in arranging their rotation for the rest of the week. They can slot in Megill or another pitcher on Thursday, Friday or Saturday.

Blackburn had hoped to avoid the IL, but when he had trouble playing catch Sunday, the Mets figured a timeout was best. “I wouldn’t say it was great,” Blackburn said. “It was definitely still some tenderness, some swelling and all that .  .  . There’s still a lot of stiffness and soreness.”

The Mets brought back reliever Huascar Brazoban to fill Blackburn’s roster spot. He had been sent down to Syracuse on Friday.

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