LenDale White is out for the season after rupturing his right Achilles' tendon during Thursday night's preseason finale at Minnesota.
"He's disappointed, of course, because he put so much time and effort into getting back on the field and getting another opportunity to play the game he loves," Brantley told The Associated Press on Friday. "But he's been very positive and will get through this fine."
Brantley said White is confident he can return to the NFL next season: "Of course. LenDale is a very focused individual, and he has his mind set on coming back and finishing the business he started."
White, who was trying to revive his career with his hometown team after a fallout in Tennessee and a short stay with the Seattle Seahawks, was injured during the second quarter of the Broncos' 31-24 preseason loss to the Vikings.
White was signed in Denver after Knowshon Moreno (hamstring) and Correll Buckhalter (back) were hurt in training camp last month. He had been released by Seattle, where Pete Carroll, who coached him at USC, is running the show.
Although he sprained an ankle two days after his arrival in Denver, White had come back strong. He scored twice in the preseason, including a 2-yard run Thursday before he was hurt on a 9-yard jaunt.
The Broncos were hoping it was just another ankle injury that could heal in September -- White already was scheduled to sit out the first four games of the regular season, his punishment for violating the league's substance-abuse policy. And White said after the game that he expected to be back by the time his suspension was over.
"It's not serious at all," White said Thursday of his injury. "I definitely have at least four weeks to get better, so I'm looking at that as a positive."
Now White faces an arduous recovery, and there's no guarantee he'll ever get back on the football field. Many a running back has seen his career ended by a ruptured Achilles' tendon.
ESPN and Pro Football Talk first reported the seriousness of White's injury Friday on Twitter.
The Broncos could bring back Justin Fargas, whom they released last week, or scour the waiver wire Saturday when teams must trim rosters to 53 players. With Denver's top three tailbacks sidelined for much of last month, Lance Ball capitalized on his carries to seemingly nail down a roster spot.
Although Buckhalter returned to action this week, Moreno's first competitive carry this year won't come until the Broncos' Sept. 12 season opener at Jacksonville.
Also Friday, NFL Network insider Jason La Canfora cited a league source in reporting that the Broncos are shopping cornerback Alphonso Smith. The team is seeking a fifth-round draft pick in return for the second-year pro, who it took in the second round in 2009.
The Associated Press contributed to this report.