PASADENA, Calif. -- "CSI" finished last season as the No. 1 drama on television, a position it's held for several years running.

Yet CBS chief Nina Tassler on Saturday said -- with a straight face -- that the show might not be the favorite in its timeslot in the fall. "Who would have thought 'CSI' would be the underdog?" she asked reporters at the Television Critics Association press tour.

The cause of her angst is ABC's "Grey's Anatomy," which ABC has moved into the 9 p.m. Thursday timeslot that "CSI" has dominated for most of its time on the air. "Grey's" is coming off a very strong second half of the season, which was fueled by a post-Super Bowl episode that grabbed better than 38 million viewers.

While Tassler knows that two hit shows can co-exist -- see "Survivor" and "Friends" or "American Idol" and "Lost" -- "we expect to be dinged by 'Grey's' a little bit," she says.

Still, "CSI" drew an average audience of 25.2 million viewers a week last year, more than 5 million better than "Grey's Anatomy," which averaged a little under 19.9 million. The hospital drama did perform slightly better in the key adults 18-49 demographic, drawing an 8.7 rating for the season to "CSI's" 8.2.

Such figures caused some critics to wonder whether the "underdog" label really fits "CSI." Tassler admits she doesn't expect her show to fall to second place, but, she repeats, "We do expect to be dinged."