Ready or not, here it comes.

The Pittsburgh Steelers’ 2021 season opener arrives Sunday with a 1 p.m. kickoff in Buffalo.

With fans being allowed back in full capacity this year — at least for the early part of the season — the stadium in Orchard Park will be packed with 70,000 fans primed for a big run out of their Bills.

The Steelers have playoff hopes of their own. But they have a few obstacles to overcome first.

When is Stephon Tuitt coming back?

Is Alex Highsmith healthy?

Will their cornerback play opposite Joe Haden stand up against pass-happy opponents?

Now that he has his contract — but having no physical contact on the field during preseason camp — how long will it take T.J. Watt to return to his normally productive self?

Then there’s the biggest question of all: Will the offensive line block anybody for any length of time?

The fate of the Steelers’ season may well rely on a positive answer to that question. It’s been a long time since Pittsburgh entered the start of a regular season with so many unknowns up front.

Kendrick Green, the Steelers’ center, is a rookie with not much experience playing that position. Dan Moore, the left tackle — the position most responsible for protecting Ben Roethlisberger’s blind side — is also a rookie.

Kevin Dotson, the left guard, is a second-year guy and has shown the most promise on this line. Trai Turner, the right guard, is an eight-year NFL veteran who made the Pro Bowl five successive years (2015-19).

But he is coming off an injury. Still only 28 years old, Turner could prove to be an anchor up front ... or he could have another year of battling injuries.

Right tackle Chukwuma Okorafor is in his fourth season and has made 19 starts for the Steelers. He was originally counted on to play the left side this year, but that didn’t work out.

Veteran tight end Eric Ebron is known more for catching passes — or dropping them — than he is blocking. Rookie tight end Pat Freiermuth is also proving to be a good target in the red zone. His blocking skills at the NFL level remain an unknown.

Anyone who follows football knows the success of an offense begins up front. The Steelers selected the best running back in this year’s draft in Najee Harris.

Harris ran behind a high-quality line at Alabama. He’s running behind a line in Pittsburgh that may still be under construction.

Harris needs to be sprung at the beginning of a play before he can have a chance to showcase his abilities. Is that going to happen?

Roethlisberger may or may not be able to adjust to Matt Canada’s offense and prove he can still perform at a high level at age 39. Again, will his line give him sufficient time to prove he can still play?

No one can truly answer these questions.

Those answers will begin to surface on Sundays — beginning with this one.

John Enrietto is sports editor of the Butler Eagle.