ST. LOUIS -- The Nationals will be without manager Dave Martinez for at least Monday night’s series opener against the Cardinals after he underwent a cardiac catheterization to help diagnose the chest pains that caused him to leave the dugout during Sunday’s 7-0 victory over the Braves.

Martinez will remain in Washington for additional testing; there is no timeline for his return. Bench coach Chip Hale will serve as manager in his absence.

“Speaking to [Martinez] today, it really reassured me that he’s doing great,” said general manager Mike Rizzo, who described Martinez as upbeat on the phone. “He’s a tough, strong guy. I think that looking at what transpired today, we’re happy and optimistic and hoping that he’ll be able to make a full recovery.”

Per the Mayo Clinic, a cardiac catheterization is a procedure in which a long thin tube is inserted in an artery or vein in the groin, neck or arm and threaded through blood vessels to the heart, enabling doctors to diagnose issues. The recovery time is usually quick, with low risk of complications, but the Nationals are expected to give Martinez, who turns 55 later this month, all the time he needs.

Martinez first told some members of the coaching staff he was feeling chest pains while in the dugout during Sunday's game. He was initially examined by the training staff before he decided to get it checked out. He left around the sixth inning for the hospital as a precaution, a discreet exit many of his players did not even realize until sometime near the end of the game.

“I don’t know how different it’ll be without him, but ... that easygoing attitude and positivity that he brings, I think, is always good for us,” shortstop Trea Turner said prior to Monday's game. “No matter if we’re up by 10 or down by 10, he’s the same guy. Like I’ve said throughout this year, that’s one thing that we really, really love about him -- he’s always the same guy. And he’s positive as well. We’re going to miss that, and hopefully he’ll be back soon.”

Martinez's absence leaves the Nationals without their manager during a critical stretch, the start of a six-game road trip to St. Louis and Miami, as they cling to the top Wild Card spot in the National League. Martinez has gone 164-146 in his two seasons as the Nats' manager, a tenure that has not been without criticism for his bullpen management and decisions.

Hale does have dugout experience, and not just managing the team after Martinez’s three ejections. He was the manager of the D-backs from 2015-16 and went 148-176. This winter he was a finalist for the Orioles' managerial job, which ultimately went to Brandon Hyde. Hale will be getting some extra assistance, as first-base coach Tim Bogar will serve as his bench coach while assistant hitting coach Joe Dillon mans first base.

In Martinez’s absence, Hale attempted to keep things as close to normal as possible. Instead of sitting in the manager’s office, he bounced throughout the clubhouse prior to the game as much as usual. He texted with Martinez earlier in the day, with Martinez sending in the lineup. Hale expects to run things during the game the same way Martinez would have.

“The players we have are what we have,” Hale said. ‘You can’t create anybody new here or change it. So the way Davey’s been running the game is pretty much how I’ve run games before.”