According to a team release, Vickers was diagnosed with a "medical condition" and continues to undergo testing and further evaluation, forcing him to miss this weekend's event.
Mears has been called up at short notice to fill in for him and will start his third race of the year, having competed at Bristol for Keyed Up Motorsports and for Tommy Baldwin Racing at Richmond. He had also been on standby for Denny Hamlin at Phoenix following Hamlin's knee surgery, but did not drive during the race.
"It is unfortunate that I will not be able to participate in the Dover race," said Vickers. "Casey is a good friend of mine, and I know he will do his best for the #83 team this weekend."
Jay Frye, Red Bull's general manager and vice president, said Vickers' recent diagnosis is just a "minor setback" and expects Mears do to a good job in the team's #83 car this weekend at the track known as the 'Monster Mile'.
"Our main concern right now is with Brian and his health and recovery," Frye said. "All things are looking good at the moment; this is just a minor setback. We appreciate Casey filling in this weekend and know he will represent the team well."
Johnny Sauter is expected to return behind the wheel of the #36 car of Tommy Baldwin Racing, which he raced at Talladega, as Mears was initially entered to drive it this weekend.
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