Henderson had surgery in Phoenix after breaking his left thigh bone in Sunday night's loss at Arizona. He had been in a hospital, but he was cleared Wednesday to come back.
"He's a man of few words, but he's in good spirits by all indications," coach Brad Childress said.
Henderson's younger brother, Erin, held his hand as he taken off the field in a cart after his leg bent in a gruesome-looking direction. He stayed with him overnight before returning to Minnesota.
Erin, a backup linebacker, was impressed by how calm E.J. remained despite the intense pain and the realization his season was over. E.J. was beginning to play at his past level after coming back from a severe foot injury that required surgery and kept him out of the last 12 games and the playoffs last year.
"One of the first things E.J. said to me was, 'I guess I'll have to sit back and watch you guys make this push to the Super Bowl,'" Erin said. "In a situation like that, it's crazy for somebody to be as selfless as he was and just kind of look at it in the light that he looked at it. That was encouraging to everybody."
It's too early to determine a timetable for rehabilitation, but Erin expressed confidence his brother would resume his career.
"I know he'll be back out here," he said. "As bad as the injury was, it could have been worse."
Henderson was placed on injured reserve Wednesday and linebacker Jeremy Leman was signed to the practice squad. In other roster moves, the Vikings signed practice squad tight end Garrett Mills to the active roster and signed offensive tackle Drew Radovich to the practice squad. They released cornerback DeAndre Wright.
Rookie Jasper Brinkley will take Henderson's place as the starting middle linebacker.
Henderson wasn't the only player hurt against the Cardinals. The Vikings listed 13 other players, including 12 starters, on their injury report Wednesday. Safety Tyrell Johnson (concussion), right tackle Phil Loadholt (shoulder) and running back Adrian Peterson (foot/ankle) did not participate at all.
Childress wouldn't get into specifics about any of the injuries, but quarterback Brett Favre indicated Loadholt dislocated his shoulder.