The team said the injury will sideline Tucker for "several weeks" and possible the season.
Tucker suffered the injury Wednesday night in the first quarter of the Bears' final preseason game at New England. It originally was diagnosed as mild sprain, but an ultrasound Friday morning revealed a torn posterior tibialis tendon.
"We know he's going to be out for a little while here obviously because he's going to undergo surgery," said Coach Dick Jauron. "We'll just wait and re-evaluate it after the surgery."
Tucker appeared to be in shock.
"I'm at a complete loss for words," he said. "I'm in total ... I don't know."
Tucker was trying to bounce back after missing the final 11 games last season because of a dislocated left ankle and fractured left fibula against Green Bay.