Seattle coach Jim Mora said the Seahawks have to prepare as though they won't have Hasselbeck for Sunday's game against the Chicago Bears.
Backup Seneca Wallace would play if Seattle's three-time Pro Bowl quarterback can't go. Wallace finished the game on Sunday.
Hasselbeck was hit hard in the back by Patrick Willis near the goal line during the first half of the Seahawks' 23-10 loss. The Seahawks are encouraged that the injury was not more severe, a league source said.
Hasselbeck rejoined his teammates for the two-hour flight home shortly after Seattle's 23-10 loss in San Francisco.
Doctors tested him for lung, liver and kidney damage and did not find any, according to the source, but they did discover the rib fracture, making Hasselbeck the second quarterback in two weeks to fracture a rib. Philadelphia's Donovan McNabb suffered the same fate in the Eagles' opener and sat out his team's game against New Orleans on Sunday.
On Sunday night Hasselbeck posted on Twitter: "Going to be alright. Thx to staff at Stanford ... ." He also attached a picture taken of him lying on a gurney soon after the injury.
Adam Schefter is an ESPN NFL Insider. Information from The Associated Press was used in this report.