Brandon Sproat seems to be using his arm to send a “message” to the Mets that he is ready, according to manager Carlos Mendoza.

That message is being delivered at a time there is question whether Kodai Senga will remain in the rotation.

Senga’s struggles continued during a 4 ²/₃-inning, five-run disappointment Sunday, after which Mendoza would not immediately commit to the struggling one-time ace making another start.

“We just got done with the game,” Mendoza said after the 5-1 loss to the Marlins at Citi Field. “We’ve got to get him right, obviously. I’m pretty sure we’re going to have some discussion what’s next for him. But our job is to get him right. It’s been a struggle.”

After a brilliant beginning to his season and a hamstring strain in June, Senga has returned and not looked like himself in nine starts in which he has a 5.91 ERA.

Including Senga, the Mets already have six starters in their rotation, so a summon of Sproat is not a guarantee — but it does appear to be getting more likely considering several downturns on the major league staff and Sproat’s own acceleration.

Sproat — who entered this season as the organization’s top pitching prospect but was beaten to Queens by Nolan McLean and Jonah Tong largely because of his struggles in the first half — struck out nine and allowed three hits and two walks over seven shutout innings Saturday as Triple-A Syracuse beat Yankees affiliate Scranton/Wilkes-Barre.

Shortly after Saturday’s loss, Mendoza heard about Sproat’s night.

“We’re watching,” Mendoza said. “It’s good to see those guys continue to put themselves in a position where, ‘Hey, if there’s a need, I’m here.’ And I think that was a message from Sproat [Saturday] to all of us here. Like, ‘Hey, man, I can do this, too.”

McLean and Tong are doing it, combining for four starts and four victories as they have joined the six-man group fairly seamlessly.

The Mets would not bring up a seventh starter without a plan to condense a rotation that houses Senga, Sean Manaea and Clay Holmes, the latter two owning stuff that has continued to impress but who have not been able to pitch deep into games.

David Peterson, who has been the ace for much of this season, has a 7.56 ERA in his past five games.

Mendoza has said that the starting pitchers are in a competition that is “fluid,” only committing to each member making another start through Tong’s next outing, which lines up for Friday in Cincinnati.

It is possible that Sproat — who had a 5.95 ERA through June 22 before turning a corner and ripping off a 2.44 ERA with 70 strikeouts in his past 59 innings — figures into the equation at some point.

It is also possible that Sproat, who last week pitched behind an opener, can be converted into a multi-inning reliever.

The Mets can call up one position player and one pitcher Monday, when September arrives.

That pitcher almost certainly will not be Sproat because he is not rested.

Among pitchers the Mets can summon Monday who are both 40-man members and are eligible to be called up are Alex Carrillo, Justin Garza, Justin Hagenman, Dom Hamel, Jonathan Pintaro and Austin Warren.

Intriguing and hard-throwing prospect Dylan Ross is not on the 40-man roster but could be added.

Tylor Megill is expected to receive at least one more rehab start before becoming an option.

As for the extra position player, the Mets are going with Luisangel Acuña, as The Post’s Jon Heyman reported Sunday night that he would be promoted back to Queens to provide defense and versatility.