Anderson will undergo arthroscopic surgery on his injured left knee this week, Jared Diamond of The Wall Street Journal reports.
Anderson's left knee inflammation sparked up again in his first start back from the disabled list Sunday, forcing the Rockies to place the 27-year-old back on the 10-day DL. They're now deeming the injury serious enough to warrant surgery, so the left-hander will go under the knife this week and reportedly be sidelined for at least the next four weeks.