NASHVILLE, Tenn. - The players' association has filed a grievance over the Washington Nationals' four-game suspension of Jonathan Papelbon that followed the pitcher's fight with teammate Bryce Harper.

The grievance was filed shortly after the suspension was announced Sept. 28, costing Papelbon $284,153 of his $13 million salary.

"That's business. It's not personal between Papelbon and the Nationals, or Nationals to Papelbon," Washington general manager Mike Rizzo said Monday.

Unless settled or withdrawn, the grievance would be heard by arbitrator Fredric Horowitz, most likely during spring training.

On the next-to-last weekend of the season, Harper flied out and headed to the dugout, where he and Papelbon exchanged words. The argument escalated, and Papelbon reached out with his left hand and grabbed Harper by the throat. Papelbon shoved the outfielder toward the bench with both hands.

Rizzo said Harper, the NL MVP, had spoken with Papelbon since the end of the season, as had some Nationals coaches. Papelbon, a six-time All-Star acquired from Philadelphia in late July, is guaranteed $11 million for next season.

"Pap's a part of this team. He's on our roster. He's a really good late-inning pitcher. He's had a great career, and we're glad he's on the club and can't wait to see him closing out games again," Rizzo said.

A 35-year-old right-hander, Papelbon displaced Drew Storen as Washington's closer. Rizzo said teams have inquired whether Papelbon is available in a trade.

"At this stage of his career, with the contract he has, there's been interest in him. There's been interest in several of our relief pitchers," Rizzo said.

In an effort to improve the bullpen, Washington has agreed to a $7 million, two-year contract with 34-year-old left-hander Oliver Perez, a deal awaiting finalization. Perez was 2-4 with a 4.17 ERA in 70 relief appearances this year for Arizona and Houston.

"He gives you a really good left-on-left guy, and if he falls back to where he was two years ago, he was good against both sides side of the plate," Rizzo said.