The Mets placed Tomas Nido on the 7-day injured list with a concussion before Saturday’s game against the Braves. The concussion was a result of the catcher getting drilled in the back of the head on a Josh Donaldson backswing during the sixth inning of Friday night’s loss to Atlanta.

Rene Rivera was recalled from Triple-A Syracuse to take Nido’s spot on the roster.

Nido was evaluated by team doctors on Saturday. He initially stayed in Friday’s game after being checked out by trainers and finished the sixth inning behind the plate with Jacob deGrom on the mound, but was replaced by Wilson Ramos in the next inning.

Ramos started Saturday and extended his hitting streak to 18 games with a sixth-inning single in a 9-5 loss to the Braves at Citi Field.

It’s the longest single-season hitting streak by a Met since Moises Alou’s 30-game streak in 2007.

Rivera most recently played in the majors last season with Atlanta. He spent much of 2016 and 2017 with the Mets and signed a minor league deal to return in March. He played 97 games with Syracuse this season before being called up.

Jed Lowrie (left knee) played in the field for the first time in his rehab stint when he started at second base Saturday for Single-A St. Lucie. He got Friday off.

It was Lowrie’s third rehab game after he was shut down in May. In four innings, he went 1-for-2.

Since signing a two-year, $20 million deal in the offseason, the 35-year-old Lowrie has dealt with a variety of leg injuries after being an All-Star a year ago in Oakland.

Brandon Nimmo (neck) got Saturday off in his rehab stint with Triple-A Syracuse.

Mickey Callaway said he was unsure whether Nimmo would be able to make it back to the Mets before rosters expand on Sept 1.

“It’s hard to put an exact timeline on when he’s gonna be available, but he is progressing,’’ Callaway said. “He feels good at the plate and looks good, according to scouting reports.”

With Saturday’s return of Jeff McNeil from a left hamstring injury, manager Mickey Callaway said he would soon have some tough decisions figuring out not only where to play McNeil in the field, but also where to slot him in the lineup.

Callaway noted he has liked Amed Rosario in the leadoff spot and Joe Panik hitting second.

Though McNeil was activated after a brief rehab stint, the Mets opted to not put him in the starting lineup, giving Callaway more time to determine where McNeil would hit.

“That’s a tough one,’’ Callaway said. “I have to continue to think about that.”

To make room for McNeil, the Mets designated outfielder Aaron Altherr for assignment.

The Mets didn’t call up a pitcher despite using seven relievers in Friday’s 14-inning loss to the Braves.

“We went through all the scenarios,’’ Callaway said of the decision. “The good part is we had five relievers [Friday] in a five-inning span that threw 49 pitches. We’ll see who else is available.”

The Braves signed former Yankee Francisco Cervelli after he requested his release from Pittsburgh.

He started the game at catcher for Atlanta, despite having suffered at least six concussions in his career.

Cervelli wanted to finish the season with a contender and demolished the Mets with three hits — two doubles — and three RBIs. He also threw out Amed Rosario trying to steal second.