Brennan's agent, Ryan Tollner, issued a statement that said Brennan was transported to Honolulu for further medical treatment after being taken to Kona Community Hospital. Brennan's condition was serious, Tollner said.
His father, Terry Brennan, told KHON-TV by telephone from California that he suffered three or four broken ribs and head injuries.
Brennan, 27, of Kona, was a passenger in an SUV driven by Shakti Stream, 27, of Kona, when she crossed the centerline on Queen Kaahumanu Highway near Makalawena and collided head-on with sedan driven by a 47-year-old Waikoloa woman, police said.
Stream also was taken to Kona Community Hospital, while the unidentified woman was transported to North Hawaii Community Hospital.
"Colt's family asks that the public is respectful of the hospitals and medical staffs focused on treating the individuals involved in this accident," Tollner said.
Police opened two negligent injury investigations. The cause of the crash was under investigation and it wasn't known if speed, alcohol or drugs were factors in the crash, police said.
Rich Miano, a University of Hawaii coach, told KGMB-TV and KHNL-TV the team would be thinking of Brennan when it hosts San Jose State at Aloha Stadium on Saturday.
"For years we've known Colt Brennan - all we've seen is triumph and victories, record-setting and smiles, always saying the right things, just positive things for the state of Hawaii," Miano said. "So this is obviously kind of a sad event."
Brennan, who finished third in the voting for the Heisman Trophy in 2007, was Washington's 2008 sixth-round draft pick. He was released by the Redskins before the start of training camp this year. He was then released by the Oakland Raiders, and last month he had a workout with the Houston Texans.
While at Hawaii, Brennan became the NCAA career leader in touchdown passes, throwing 131 TDs from 2005-07.
Brennan developed a solid fan base in Washington despite never playing in a regular season game in two seasons. He spent 2009 on injured reserve after hip surgery, then had knee surgery in March, which set him further back.