As the Phillies sat through a rain delay Wednesday night, there was concern for the health of catcher J.T. Realmuto.

Realmuto, the player the Phillies can least afford to do without, left the game after taking back-to-back foul balls off the mask during Los Angeles Dodgers first baseman Max Muncy’s at-bat in the first inning. The second ball knocked the mask off Realmuto’s face, dropped him to one knee, and prompted an athletic trainer to check on him.

Major League Baseball stipulates that players who leave a game with a head injury undergo tests for a concussion. Realmuto was going through those protocols Wednesday night, according to manager Joe Girardi, and the Phillies were awaiting the results.

“He goes through a test and you wait for MLB to respond to the test,” said Girardi, adding that Realmuto was “day-to-day” and “questionable” for Thursday’s series finale. “We’ll have to see how he is [Thursday].”

If the Phillies have to place Realmuto on the concussion list, he will miss at least seven days.

Despite initially staying in the game, Realmuto was lifted for pinch-hitting backup catcher Andrew Knapp in the bottom of the first. Television cameras spotted Realmuto going down the tunnel to the Phillies’ clubhouse with head athletic trainer Paul Buchheit.

Rafael Marchan, the likeliest catcher to be called up if Realmuto is placed on the concussion list, wasn’t pulled from triple-A Lehigh Valley’s game at Scranton/Wilkes-Barre. It seems likely, though, that he will be on his way to Citizens Bank Park just in case.

Realmuto is batting .268 with 13 homers, 52 RBIs, and an .804 OPS in 92 games. Lately, though, he has been among the Phillies’ hottest hitters. During the team’s recent eight-game winning streak, he went 12-for-29 (.414) with three doubles, two homers, 10 RBIs, and a 1.176 OPS.

The Phillies reinstated left fielder Andrew McCutchen from the injured list before Wednesday night’s game. But they are playing without first baseman Rhys Hoskins, who is sidelined with a strained left groin.

Losing Realmuto, even for a week, would be a blow to the middle of the order as well as a pitching staff that values his leadership behind the plate.