Alvarez immediately left the game. An X-ray came back negative, and the right-hander has made steady progress since.
Miami had considered pushing Alvarez back a day or so, if he wasn't feeling ready.
"We're anticipating Henderson will be fine," manager Mike Redmond said. "He's feeling better each day. He should be fine to make his start."
An All-Star for the first time, Alvarez has emerged as Miami's top starter since Jose Fernandez underwent Tommy John surgery in May.
"We got lucky, because it caught Henderson between the muscle and the shin," Redmond said. "I think it got more muscle than bone. It blew up quickly on him. It was sore, of course. I think he's fine. We can't lose anybody, but especially him. It's good that he's fine."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter