Kevin Magnussen will make his IndyCar debut at Road America with Arrow McLaren SP.
The Danish driver will join ex-Haas F1 team-mate Romain Grosjean in the premier single-seater category in America as a replacement for Felix Rosenqvist, who was injured in a crash at last weekend's Duel in Detroit event.
At the same event, Magnussen tasted his first success in IMSA sportscar racing with a pole position and win alongside Renger van der Zander.
A statement from Arrow McLaren SP read: "Following an evaluation by the INDYCAR Medical Team, Felix Rosenqvist has not been cleared to race at this weekend’s REV Group Grand Prix at Road America.
"Felix will continue to be supported by the team as he progresses in his recovery.
"Felix will be replaced for the REV Group Grand Prix by Kevin Magnussen, who will be making his INDYCAR debut.
"Magnussen made 19 starts for the McLaren Formula 1 team in 2014, including a career-best finish of second at the Australian Grand Prix that year."