Speaking after his team's 6-2 loss, Astros manager Dusty Baker said Alvarez had shortness of breath, which was made worse by the smoke in the air after the Braves shot off fireworks at Truist Park.
Alvarez was released from the hospital Friday night and all tests performed came back normal. He was at the ballpark Saturday and will undergo further evaluation.
Alvarez departed the Friday night game under his own power with two outs in the bottom of the fifth inning. There was a pause in the action when Braves rookie Vaughn Grissom fouled a ball off his foot and was being tended to by an athletic trainer.
That's when Alvarez, who is batting .295 with 31 homers and 77 RBIs, made his break for the Houston dugout.
"I'm glad we got him out when we did," Baker said Friday night. "I looked up and he was in the dugout. It was kind of a scary moment. It could be anything. They said he's doing fine at the moment."
Baker said no one in the Astros' dugout knew Alvarez, an American League All-Star this year and the 2019 Rookie of the Year, was in any distress.
"We didn't see anything," Baker said. "I just looked up in the dugout and he was there. After that we had to take it into emergency action to find out what's wrong and then the emergency crew came over and took him to the hospital."
Losing Alvarez, who ranks first in AL on-base percentage and second in homers, slugging percentage, OPS and runs, for any length of time would be a big blow to Houston. The AL-leading Astros are 77-44 and primed for another deep postseason run. They lost in the World Series last year to Atlanta.
"He's a big, big part of this team," Baker said. "He's our big boy in the middle, so we're not thinking about losing him. We're thinking about getting him back and hopefully he'll be all right tomorrow.''
Information from The Associated Press was used in this report.