It is "not realistic" to expect New England Patriots tight end Rob Gronkowski, who underwent offseason back and forearm surgery, to be ready to play in the team's regular-season opener against the Bills in Buffalo, sources familiar with the situation said Monday.

"It's a huge stretch to think he could play against the Bills," the source said.

Despite that, another source said Gronkowski "looks great, is doing great" during his workouts at the Patriots' training facility, where he has been running and lifting.

Sources tell ESPN it's "not realistic" that Rob Gronkowski, left, will be ready to take the field with Tom Brady for the Patriots' opener at Buffalo. AP Photo/Charles Krupa

Progress is being made, but not enough for there to be much confidence Gronkowski will be ready for the start of this season. Before then, one of the biggest roster decisions New England will have to make is whether to carry Gronkowski on the 53-man roster or place him on the physically unable to perform list, which would automatically sideline him for at least the first six games.

What the Patriots do with Gronkowski also could impact quarterback Tim Tebow, who is on the roster bubble in New England. Should New England place Gronkowski on the PUP list, it would give the Patriots additional roster flexibility that could mean carrying a third quarterback.

But if Gronkowski is not placed on PUP and stays on the roster, that will be one fewer spot available on the Patriots' roster.