Rest assured this is the sort of time where you can be happy that the Penguins have these long waits in between games. Sam Kasan reported earlier today on the Penguins' official site that Brent Johnson didn't practice today and Evgeni Malkin left the ice with about 20 minutes to go.
He later followed up in his practice report with this quote from Dan Bylsma:
"Brent was sick and 'Geno' has nothing different than he's had for the last week," Bylsma said. He added about Malkin, "He had some discomfort on the ice so we took the opportunity to rest it."
Given the fact that the Pens don't play again until Wednesday night, in all likelihood Johnson should be good to go if he's needed. As for Malkin, the hope is that whatever mysterious injury/ailment is bothering him will gradually heal up by then or, at the least, not be as bad. As is typical with the Pens, and most teams in hockey for that matter, there's no saying what the exact problem is, although prior speculation has led to believe it's a knee/lower-body injury.