Red Sox closer Jonathan Papelbon is expected to sign a four-year, $50 million dollar deal with the Philadelphia Phillies, according to a report.

According to ESPN, Papelbon, who has been the Red Sox's closer for the past six years, will be headed to the Phillies in the monster deal pending a physical with the team.

The deal also includes a vested option that could make it a five-year, $60 million deal, according to Sports Illustrated's Jon Heyman.

Papelbon helped guide the Red Sox to a World Series title in 2007, but struggled a bit during the team's historic collapse at the end of the 2011 season. The massive deal with the Phillies, which lost in the National League Divisional Series to the St. Louis Cardinals, is the largest ever for a relief pitcher.

His average salary of $12.5 million doesn't match Yankees closer Mariano Rivera's $15 million a year, but his overall deal tops the previous high of the five-year, $47 million for Toronto Blue Jays closer B.J. Ryan.

The 30 year-old closer had 219 saves and made four All-Star teams in his time with the team. His replacement could be relief pitcher Daniel Bard, if the Red Sox decide to stay within the organization. If not, former Phillies closer Ryan Madson could be an option at a discount compared to Papelbon's record breaking contract.

The Phillies had indicated interest in resigning Madson, but vigorously pursued Papelbon once a deal with Madson fell through.

In addition to paying Papelbon a record deal, the Phillies might also have to give up their first round draft pick in this year's MLB Draft to the Sox. Based on the current free agency rules, Papelbon as a Type A free agent requires a first-round draft pick as compensation, but ESPN reported that labor unions are fighting to reduce the amount of free agents that would require a draft pick compensation.