Michalek, who was on pace for a career season, collided with teammate Erik Karlsson in the second period Tuesday night in Buffalo and didn't return.
MacLean said Michalek, who had scored just 69 seconds into the game, was day to day with the concussion and didn't believe it would be a long-term absence.
"Right now we have to follow the concussion protocol, so right now it's day to day," MacLean said. "It's based on as long as he's symptom-free. He felt way better (Wednesday), so we'll see how it goes."
Just Tuesday, the Philadelphia Flyers announced that the NHL's leading points scorer, Claude Giroux, was out indefinitely with a concussion. Flyers captain Chris Pronger is out with concussion-like symptoms, as is Penguins star Sidney Crosby, among other players.
"I read the guy's pass and stepped up and I think Milo was coming full speed to back check," Karlsson said. "I was only looking for their guys and not ours, and we collided pretty hard there. We were both going forward. It's just bad luck. I didn't see him coming."
Information from ESPN.com's Pierre LeBrun was used in this report.