Papelbon had a strong start to the season for the Nationals but struggled mightily in his last five outings before he was released on Saturday, as his ERA spiked from 2.56 to 4.37 over that span.
The Red Sox -- and any other team in the Majors -- could sign Papelbon at the pro-rated Major League minimum for the remainder of the season. The Nationals are still on the hook for the balance of his $11 million salary for 2016.
Farrell had a strong working relationship with Papelbon while serving as his pitching coach from 2007-10. Papelbon pitched for Boston from 2005-11, notching 219 saves.
Though Papelbon isn't that caliber of pitcher anymore, Farrell still thinks the righty has a chance to be effective, particularly in an environment he once had great comfort in.
"With the exception of a stretch in July, where maybe the performance was sub or less than what Pap has been maybe accustomed to, he's been an effective pitcher," Farrell said. "Coming back into Boston, if that were to happen, he's very well aware of the environment, the expectation, so we'll see where that goes. There's been internal discussions, but really nothing else to report."
Brad Ziegler, Junichi Tazawa and Matt Barnes are Boston's three top setup men with Koji Uehara's status uncertain for the rest of the season due to a right pectoral strain.
"Pap is a unique guy in many ways," said Farrell. "But a guy that thrives in the moment, thrives to be in critical spots in the ballgame. While that closing role may be a thing that's behind him, the intangibles of the competitor haven't changed."
Red Sox president of baseball operations Dave Dombrowski has acknowledged the club has investigated the possibility of acquiring Papelbon, but he didn't feel it was appropriate to comment beyond that. The Cubs could also have interest in Papelbon, particularly considering the presence of former Boston executives Theo Epstein, Jed Hoyer and Jason McLeod.
A return to Boston would allow Papelbon to rejoin two good friends (Dustin Pedroia and David Ortiz) in another push for a World Series championship.
"Certainly the electricity of Fenway Park brings out the best in everybody," said Farrell, "and you see it when visiting teams come in. We see it in our own guys when we come off of a road trip or after a long night the previous night. Our fans energize every player who takes the field. If this were to come to fruition, to what extent that could add some adrenaline [for Papelbon] remains to be seen."