ATLANTA -- With Noah Syndergaard on the injured list, the Mets will turn to one of their key offseason acquisitions for a boost. The team plans to call up right-hander Walker Lockett on Thursday to make his Mets debut at Wrigley Field.

Lockett, 25, missed the first six weeks of this season due to a right arm injury, but he has since posted a 3.28 ERA in four outings at Triple-A Syracuse. The Mets acquired him from the Indians in a trade for catcher Kevin Plawecki last winter.

“He’s been throwing the ball over the plate,” manager Mickey Callaway said. “He’s healthy. He’s the guy that we brought into the organization this offseason to be that sixth starter, that depth starter that we knew we’d need at some point. [Thursday] is going to be his opportunity to show what he can do.”

Entering Spring Training, team officials considered Lockett a crucial part of their rotation depth. He is now one of the last men standing on that list, with Corey Oswalt on the Minor League IL, Hector Santiago and Kyle Dowdy no longer in the organization, and Chris Flexen converted to relief work. The Mets’ remaining upper-levels depth includes veteran Ervin Santana, whom they signed last month to a Minor League deal, and No. 3 prospect Anthony Kay, whom they do not consider quite ready for the Majors.

New York’s most realistic alternative for Thursday’s start was reliever Wilmer Font, who threw three innings and 55 pitches in his most recent outing Sunday. The Mets preferred Lockett because he is capable of pitching deeper into the game, throwing 92 pitches in his last start.

“When you’re using a spot starter like this, you throw him out there and see how effective he can be,” Callaway said.

While Syndergaard has been working out daily at SunTrust Park this week, the Mets are going to need a replacement starter for him at least twice -- once on Thursday in Chicago, and again June 25 in Philadelphia, the day before Syndergaard is eligible to return.

At least the first of those starts will go to Lockett, a 6-foot-5 right-hander featuring a low-90s fastball, a curveball, a changeup and some deception in his delivery. Lockett appeared in three games last season for the Padres, producing a 9.60 ERA in 15 innings, before San Diego traded him to the Indians in November. Two months later, Cleveland flipped him to the Mets.

“The good part is he’s pitched in the Major Leagues before,” Callaway said. “He’s not going to be making his debut. And you know what? When that’s who you call up, you’ve got to get the job done no matter what the circumstances are. It’s never easy. We always understand that. And we expect him to go out there and pitch like he did in Triple-A.”

Pitcher elects free agency

Santiago, whom the Mets designated for assignment last weekend, cleared waivers and elected free agency rather than accept an outright assignment to Syracuse. A veteran of nine big league seasons, Santiago nearly broke camp with the Mets this spring, before a poor end to Grapefruit League play cost him a roster spot. He did not earn a call-up until late May, producing a 6.75 ERA in eight appearances before the Mets designated him.

Given his Major League service time, Santiago had the right to reject an outright assignment.

Draft pick signs

The Mets on Wednesday inked second-rounder Josh Wolf to an above-slot contract worth $2.15 million, according to a source. The signing leaves them with a little more than $2 million to spend on third-round selection Matthew Allan without sacrificing a future draft pick. Although that figure is only about half of Allan’s reported $4 million draft day demand, Mets officials remain confident they can sign the standout Florida high school pitcher.

From the trainer’s room

The Mets are sending reliever Justin Wilson for tests after scratching him from a rehab appearance Tuesday due to continued elbow soreness. Wilson, who has been battling an issue in his left elbow since April, will likely undergo an MRI.

“I wouldn’t say we’re back to square one, but we shut him down because he didn’t feel like he could go,” Callaway said.

Setup man Jeurys Familia, by contrast, will not undergo an MRI because the Mets “understand what’s going on with him,” Callaway said. The team placed him on the IL on Tuesday with a Bennett lesion -- essentially a bone spur -- in his right shoulder.

Delayed reunion

Rookie reliever Stephen Nogosek did not learn until relatively late on Tuesday that he would earn his first big league call-up, leaving little time for his parents and wife to make the trek to Atlanta. Nogosek went unused in Tuesday’s game, however, giving his cheering squad a chance to make the trip the following morning

The week has been a blur for Nogosek, who flew to Atlanta without knowing for sure if the Mets would activate him.

“Just pure excitement,” Nogosek said. “I’m excited. It’s an exciting time.”