There often is one significant surprise in the annual firing-and-hiring season for NFL coaches, and this year’s semi-stunner came Wednesday. Doug Marrone opted out of his contract with the Buffalo Bills early on New Year’s Eve, making him a highly attractive coaching free agent and leaving the Bills to join the five other NFL teams searching for new head coaches.

Marrone’s contract gave him three days after the regular season ended to opt out of his deal because the Bills were sold this year from the Ralph Wilson estate to Terry and Kim Pegula. He had two seasons remaining on his four-year, $16 million contract, and a person familiar with the situation said that negotiations on a possible extension broke down before Marrone decided to leave the organization.

“Doug Marrone informed me late today that he has decided to exercise the option clause in his contract and relinquish his responsibilities as our head coach,” Terry Pegula said in a written statement released by the Bills. “We are disappointed that Coach Marrone will no longer be an important part of our organization. We thank him for all of his hard work and leadership during his tenure and wish him and his family the best with the next chapter in their lives.

“We will now begin the important process of conducting a thorough search for a new head coach as we continue to strive to reach our goal of returning to the playoffs and bringing a championship to Buffalo for our fans.”

Under the terms of his contract, Marrone receives his $4 million salary from the Bills for next season in addition to any income he might receive from another team if he’s hired elsewhere, according to the person with knowledge of the deliberations, who spoke on the condition of anonymity because he was not authorized to comment publicly on the details of Marrone’s deal.

It had been widely believed within the league in recent days that Marrone would remain with the Bills, perhaps with a contract extension, despite reports of tension existing between him and the team’s front office. Instead, he joins a pool of NFL head coaching candidates that lost its biggest name when Jim Harbaugh returned to the college coaching ranks at his alma mater, Michigan, after parting ways with the San Francisco 49ers.

Marrone spent two seasons with the Bills and coached them to a record of 15-17. The Bills went 9-7 this season but missed the AFC playoffs, extending the league’s longest postseason drought. They last reached the playoffs in the 1999 season. But Marrone drew praise within NFL circles for coaching the Bills to a winning record during a season in which the franchise was sold and the team relocated a home game to Detroit due to a massive snowstorm.

The 49ers, Oakland Raiders, New York Jets, Atlanta Falcons and Chicago Bears also are looking for coaches. Speculation immediately linked Marrone to the Jets. He is a New York native and served as the Jets’ offensive line coach between the 2002 and 2005 seasons.

A person familiar with the league’s hiring cycle said that San Diego Chargers offensive coordinator Frank Reich, a former Bills quarterback, is expected to receive strong consideration to replace Marrone in Buffalo.

If so, Reich potentially could work with Bill Polian. There has been persistent speculation that Polian, the highly respected former front office architect of the Bills, Carolina Panthers and Indianapolis Colts, might rejoin the Buffalo front office this offseason. He most recently has been an NFL analyst for ESPN.

The Bills’ decision-makers will have to figure out what to do at quarterback after the team announced Monday that Kyle Orton, the veteran who took over this season for benched former first-round draft choice EJ Manuel, had decided to retire. The Bills could turn back to Manuel or search for a replacement.