Update: Monahan is also affected by this announcement, which seems to confirm that he's not 100%, but he's playing the games anyway.
In Gallagher's case, knowing him, it takes a lot for him to miss a practice (because he is a real one), but let's wait and see. Martin St-Louis will give us more details in a press conference in the next few minutes.
At this time, there is no indication that Gallagher and/or Monahan are at risk of missing any games, but it is something to watch for.