Millwood, 36, is 2-2 with a 3.79 ERA in six starts after signing with the Rockies on Aug. 8. He spent most of the year pitching in the Minor Leagues for the Yankees and Red Sox organizations.
Tracy said the Rockies would be looking to find a starter who could consistently work six or seven innings during the offseason.
"I can promise you this: As we go forward, as early as the early part of next season, it's very, very important that we can identify somebody that you can look and say, 'You know, pretty much on a regular basis, you're going to get six or seven out of this guy every time he goes out,'" Tracy said. "It's really, really important to the success of a pitching staff and to the success of a ballclub.
"Is Kevin Millwood one of these guys? Maybe he is."
Tracy said Millwood would have a few starts to "further audition as to where his situation may stand and/or may go to as we move forward."