Tight end Rob Gronkowski is expected to undergo back surgery Friday to have a herniated disk repaired, a person familiar with the situation confirmed. The news of Gronkowski’s surgery first was reported by the Buffalo News and also was confirmed by other media outlets.

Gronkowski is expected to be sidelined for approximately two months, meaning he would not return until very late in the postseason and most likely not until the Super Bowl – if then – should the Patriots advance that far.

Four-time Super Bowl-winning quarterback Tom Brady clearly is the Patriots’ most indispensable player, even with the Patriots’ 3-1 record to begin this season while Brady served his Deflategate suspension. But a very good case can be made that Gronkowski ranks second on that list.

He is Brady’s go-to receiver and he is a matchup nightmare for opposing defenses. He is too swift and athletic to be covered by most safeties and is too big and powerful to be covered by most cornerbacks. If defenses adjust, that opens things up for other receivers, and no one knows better than Brady how to take advantage.

The Patriots have been particularly successful on offense over the years when they have had two capable pass-catchers at tight end, as they have had this season with Gronkowski and Martellus Bennett. But now Brady must make things work with Bennett minus Gronkowski.

According to ESPN, the Patriots are 15-6 without Gronkowski in the 21 regular season and postseason games he has missed, including 3-0 this season. But this isn’t about merely winning a few games. This is about attempting to secure a fifth Super Bowl triumph with Brady at quarterback and Bill Belichick as the team’s coach. The margin of error becomes ever slimmer against top competition in the postseason, and Gronkowski’s absence could make a difference.

Brady, according to the NFL Network, has a passer rating of 104.5 in games with Gronkowski since 2010, and a passer rating of 84.4 in games without Gronkowski.

Brady has played at an MVP level this season with 18 touchdown passes, only one interception and a passer rating of 116.7. He has plenty of options around him on the New England offense, with Bennett at tight end and Julian Edelman, Danny Amdendola, Chris Hogan and rookie Malcolm Mitchell at wide receiver. LeGarrette Blount is a bruising runner, and Dion Lewis and James White are effective receivers out of the backfield.

But things have been a struggle lately. The Patriots followed a loss to the Seattle Seahawks with a relatively routine victory at San Francisco but then found the going tough last Sunday at the Meadowlands against the lowly New York Jets. They trailed by 10-0 in the second quarter and by 17-13 in the fourth quarter before rallying to win, 22-17.

Gronkowski didn’t have a catch in that game and exited in the first quarter with his back injury. That was an abbreviated return to the lineup after he’d missed one game with what was described as a chest injury suffered on a hit by Seahawks safety Earl Thomas.

Brady missed two practices last week because of a knee injury and clearly wasn’t himself last Sunday. He did not dismiss a question afterward about whether he’d had trouble stepping into his throws properly because of his knee. Brady missed practice again Wednesday but was back on the practice field Thursday as the Patriots readied for Sunday’s game at home against the Los Angeles Rams.

They have a record of 9-2 and have a two-game lead on the second-place Miami Dolphins in the AFC East. They are virtually tied with the Oakland Raiders for the top seed in the AFC playoffs. Last season, remember, the Patriots followed a 10-0 start to the season with a 2-4 stretch to close the regular season, squandering the AFC’s No. 1 seed in the process. They had to go to Denver for the AFC championship game and lost to the Broncos.

That was a bitterly disappointing defeat to many in the Patriots organization who believed that the team wasted a tremendous opportunity to add to its Super Bowl largesse. Brady is 39 and, despite what he seems to think and what his ongoing on-field brilliance suggests, he won’t play forever. The chances are beginning to dwindle.

Belichick praised his team Sunday for what he called its resilience, mental toughness and ability to execute under pressure against the Jets.

The tests will get far tougher after the Rams leave Foxborough, Mass. The Baltimore Ravens arrive for a Monday night game there eight days later and the Patriots face road games down the stretch at Denver and Miami. They certainly would prefer to have the AFC’s road to the Super Bowl go through Foxborough.

The Raiders have a key injury of their own with quarterback Derek Carr now playing with dislocated pinky on his throwing hand. The Carr and Gronkowski injuries could open things up for other top AFC contenders. The Dallas Cowboys or the Seahawks would be a daunting Super Bowl opponent coming from the NFC.

If the Patriots find a way to get it done this time, they truly will have earned it.