Bell, who still has not signed his franchise tender, can't be fined for his absence from training camp because he doesn't have a signed contract. He isn't permitted to receive a long-term contract this season, because the deadline to do so for tagged players passed on July 17.
"My feeling is there's nothing to be gained by a holdout,'' Colbert told the newspaper Wednesday. "The situation won't change; it can't really change from our part on a long-term deal.
"So it hurts him not to be here. It hurts him because he's not working with his teammates, he's not getting the conditioning work that he's going to need to have a great 2017 season. And he's not working with his teammates to get acclimated to the offense -- every year it's different."
Former Steelers running back DeAngelo Williams, who was Bell's teammate the past two seasons, disagreed with Colbert's take.
Bell recently posted Snapchat videos of himself working out in South Florida. He consulted with Elite Footwork specialist Rischad Whitfield in Miami for a five-day stretch that ended this week. Bell worked on quick-twitch footwork, change of direction, body control and running back-specific drills, Whitfield told ESPN's Jeremy Fowler.
Whenever he does report and sign his franchise tender, Bell will be paid $12.12 million this season.
Bell, 25, stated his case as the game's best running back during an explosive 2016 season, when he averaged 157 yards from scrimmage, the third-best clip ever for a running back.