Meszaros should be ready to go around the time the season starts or maybe a few games later.
As for gustafsson, from what I've seen he just took a puck off the foot or ankle and there's no real damage.
From metlzer :
Gustafsson has missed the last couple weeks with an ankle injury sustained while blocking a shot. He practiced, albeit sparingly, last week so he should be ready to join the Flyers. The status of his Adirondack defense partner and Flyers teammate, Marc-Andre Bourdon is less clear. Bourdon is still sidelined indefinitely due to concussion-like symptoms.