A six-time Pro Bowl pick, Kreutz was an emotional leader and an important piece for a team coming off a run to the NFC Championship Game even if he was no longer at his peak.
He had backed off his request for a multiyear contract and was willing to take a one-year deal. Even so, the two sides couldn't reach an agreement.
Now, the Bears are turning to the 29-year-old Spencer, the No. 26 overall pick by the Seahawks in the 2005 draft. Back then, Bears director of player personnel Tim Ruskell was the Seahawks' general manager.
"You guys know how I feel about Olin," Bears coach Lovie Smith said. "He's been a great Chicago Bear for us. Every year is a different year, a different team. You have to move on, which we're going to have to do. We are going to do it. We have a good football team, and other guys will move into that role."
Kreutz told the Chicago Tribune on Sunday that he might not ever play again.
"That is a decision I am still making. I am sure I will have an opportunity," Kreutz said. "I am just not sure if I want to play for anyone else. Retirement is definitely an option."
Kreutz played down any perception of animosity between himself and general manager Jerry Angelo.
"Jerry has been good to me too. Heâs given me a lot of money and Iâve been there a long time," Kreutz said. "It felt like maybe it was time to move on. I just got that feeling. If I was right, if I was wrong, if the offer was fair. I have enough money. So the offer wasnât a big hurdle for me. It was a feel I had, just maybe they wanted to move on no matter what the offer was."
The Tribune reported that the one-year offer Kreutz turned down was for $4 million.
Like every other NFL team during this unique offseason, the Bears have been busy, adding former Pro Bowl receiver Roy Williams, running back Marion Barber, defensive tackle Amobi Okoye and punter Adam Podlesh. They overhauled their tight end corps by trading Greg Olsen to Carolina, releasing Brandon Manumaleuna and adding Matt Spaeth.
Losing Kreutz creates more questions on an offensive line that struggled last season. Chicago allowed a league-leading 56 sacks last year, with Jay Cutler taking 52 of them and suffering a concussion in the process. Things improved over the final nine games, when the Bears went with the same five players after going with four different lineups in the first seven games because of injuries and poor play.
Kreutz, however, helped keep things together even though he was no longer a dominant force. He was limited for much of the season while recovering from Achilles' tendon surgery.
Even so, not seeing him at camp the past few days was strange for his teammates. Guard Roberto Garza has been filling in at center and will likely continue to do so until at least Thursday, when Spencer can start practicing.
"(Kreutz) stands for what a Chicago Bear is," Garza said. "Tough. Hard-nosed football player. He made his teammates better."
The Associated Press contributed to this story.