The subject came up during Shanahan's weekly session with reporters who regularly cover the Broncos.
"I'll be honest with you, I was a little disappointed," said Shanahan, who held the same job with the Raiders through the first four games of the 1989 season when they were based in Los Angeles.
Managing partner Al Davis fired Shanahan after the 1989 team lost three of its first games.
"When you take a look at it, I was there 582 days," Shanahan said tongue-in-cheek. "Lane Kiffin was there 616 days. So what it really means is that Al Davis liked Lane more than he liked me. I really don't think it's fair. I won three more games and he got 34 more days of work. It just doesn't seem right."
In 13 seasons with Denver, Shanahan has a 314-159-3 overall record.
Justin Bieber crashes Drake Bell's album release party
Rosie O'Donnell unveils nearly 50-pound weight loss