"It got me in between the bone and the flesh," Alvarez said in Spanish. "It got me pretty good, but luckily I'm fine. Just a bump."
An X-ray came back negative. Alvarez is tentatively lined up to start Thursday at Atlanta. But his status will be updated after he is able to test the leg in the next few days.
"I anticipate on making the next start," Alvarez said. "I've got to give it a couple days to see how it heals, but as of now I'm looking to pitch in Atlanta."
The injury occurred when Joe Panik slapped a grounder headed up the middle. The ball smacked off Alvarez's left leg just above the ankle and then ricocheted off the pitcher's right calf.
Alvarez still recovered to bounce off the mound, field the ball and throw Panik out at first base. But immediately, Alvarez doubled over when he tried to apply weight to his left leg.
"It hurt, but I saw the ball close to me so I kept going with the play and finished it off before going to the ground," Alvarez said.
Manager Mike Redmond and assistant athletic trainer Mike Kozak dashed to the mound. Hobbled, Alvarez was assisted off the mound and headed straight to the training room.
The Marlins announced the injury as a left shin contusion, and he is listed as day to day.
Alvarez exited after 33 pitches, with 26 strikes. Sam Dyson replaced the Miami starter.
The Marlins' rotation has struggled for a few weeks, and Alvarez has emerged as the team's ace since Jose Fernandez underwent Tommy John surgery in May.
Alvarez was named to the National League All-Star team two days before the event, replacing Washington's Jordan Zimmermann.
Alvarez (6-5) was tagged with the loss Saturday. His ERA is 2.64.
"He seems like he's going to be fine," Redmond said. "We'll see as we go the next few days' progress and he goes out there on his bullpen day and see how he feels."