Treinen will have a small cyst surgically removed from his middle finger later this week, Susan Slusser of the San Francisco Chronicle reports.
The issue was minor and didn't affect Treinen's pitching at all, but the team will have it taken care of now that the season is over. Treinen compiled a 2.13 ERA for the A's after being acquired from the Nationals, and Oakland has expressed interest in using him as the closer next year.