Diagnosed with a left upper back, neck and shoulder strain, Molina described himself as a "little sore" and having "a really bad headache" about two hours after being knocked down by Harrison.
The impact came in the second inning when, with the Pirates leading, 1-0, Harrison tried to score from second on a two-out single. He barreled into Molina as Molina took a throw from right fielder Carlos Beltran.
With his left elbow up, Harrison knocked Molina in the head and onto the ground. Molina managed to hold on to the ball, and Harrison was called out. But Molina did not get up.
The training staff, several teammates and manager Mike Matheny -- a former catcher whose career ended prematurely due to concussions -- raced out to check on Molina. Molina eventually stood up, before collapsing back onto his knees. He had to be helped off the field.
"He wasn't thinking very well. He was just stunned," Matheny said. "That was basically what happens with those. You don't know exactly what's going on. You could tell right away that his neck was bothering him. He took a shoulder straight to the head. There was a lot of things that could go wrong there."
Molina came out of the game and a Pirates physician administered a Sport Concussion Assessment Tool 2 exam on Molina shortly after to see if he was showing signs of a concussion. Molina did not exhibit such symptoms, the Cardinals announced.
X-rays done on Molina's back/shoulder/neck area also checked out clean.
"It's terrifying, whether it's a teammate or anybody," teammate David Freese said of the play. "Harrison came in hard. He put the gear on him. Sometimes that happens."
Added Skip Schumaker: "That's very scary. You never want to see, in my opinion, your MVP go down, especially with a head or neck injury. You don't want to see any catcher like that."
Molina, who was already dealing with an ankle injury, has not been placed on the disabled list, but the Cardinals have summoned catcher Bryan Anderson from Triple-A Memphis to provide the Cardinals with coverage in case Molina is out for any length of time. Ryan Jackson is expected to be optioned in order to add Anderson to the roster.
The question of whether the hit Harrison put on Molina was clean elicited, as expected, different reactions from both sides.
Said Harrison: "I felt like he had the plate blocked. ... I didn't want anyone to get hurt, but it's part of the game. If they feel I did it intentionally, and tried to run the guy over and put him out ... fine. Them feeling so is part of the game, too. We play the game hard. You don't want anyone to get hurt. You feel bad, but got to move on -- that's the bittersweet part."
Cardinals pitcher Jake Westbrook hit Harrison with a pitch later in the game. The plunking prompted both dugouts to be warned.
Several Cardinals players were asked about the collision as well, and each one took middle ground. The absence of an answer got their point across.
Asked the same question, Matheny responded: "He hit him hard. Yadi did a nice job of holding on."
Molina was perhaps the only one without an opinion yet, as he had not yet seen a replay of the hit.
"Hopefully it's a good play. I have to wait and see," said Molina, who entered the night with the league's fourth-best batting average. "I was concentrating on catching the ball. I never saw him coming. The pain was on my head, but I don't know if it was straight to my head or not."
This is the second substantial collision Molina has endured in his career at PNC Park, and ironically, the other came eight years ago to the day on Tuesday. In that instance, Molina took a hard hit from Pittsburgh's Ty Wigginton. He ended up having only one at-bat during the following nine days.
"What a great play that was then and then again tonight and just as equally tonight taking a short hop and hanging on to it," Matheny said. "He's legitimately the toughest guy in the league. It's just a shame that he's down now."
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.