Broxton, sidelined since May 4 with a bruised elbow, now is likely to be shut down for the remaining two weeks of the season, having pitched only 12 2/3 innings in his free-agent season. His rehabilitation has been plagued by setbacks to his elbow and a sore back.
With the uncertainty over his health, and the emergence of Javy Guerra and Kenley Jansen in late-inning relief roles, the departure of Broxton and his $7 million salary is virtually assured.
"It's really tough," Mattingly said when asked how the club can evaluate Broxton for next season. "We haven't seen him pitch in a long time. I don't even know how to answer it. Everything is unknown. Can he bounce back without this bothering him? I'm sure he doesn't know either."
The two-time All-Star, who had 58 saves over 2009 and 2010, went 1-2 with a 5.68 ERA and seven saves this year.
Broxton joins Casey Blake (neck surgery), Rubby De La Rosa (elbow surgery), Jon Garland (shoulder surgery), Andre Ethier (knee surgery), Vicente Padilla (neck surgery) and Juan Uribe (sports hernia surgery) with season-ending injuries. It is not believed that Broxton needs surgery.
Ethier, who had minor right knee surgery on Wednesday, was at the ballpark on Thursday to begin his rehabilitation program, which will continue next week at his Arizona home.