The 2016 Indy 500 winner will join the fulltimers in the #7 Acura ARX-05, which led a Penske 1-2 at Mid-Ohio SportsCar Course last season, Penske’s first full sportscar campaign since 2009.

Fellow IndyCar driver Simon Pagenaud will continue for a second year as the endurance 'extra' pilot for the #6 Acura, alongside fulltimers Juan Pablo Montoya and Dane Cameron.

Rossi, who finished as runner-up in this year’s IndyCar championship, commented: “I have watched and raced against Team Penske in IndyCar and I have a lot of respect for the organization and what they do and how they do it.

“I really appreciate Andretti Autosport for allowing me the opportunity to represent Acura in some of the biggest sportscar races in the world. I can’t wait to work with Helio and Ricky, to learn from them and hopefully contribute to some wins and a championship for Acura Team Penske.”

Art St. Cyr, president of Honda Performance Development, added: “Alexander will be a great addition to the Acura Team Penske lineup in 2019 and all of us at Acura are very excited about our prospects for the coming season.

“When you add Alexander to the experienced team of Helio, Ricky, Juan and Dane - and with Simon returning for the endurance events – we are extremely proud of the talented and accomplished Acura Team Penske driver lineup. We look forward to our second opportunity to win the Rolex 24 at Daytona in the ARX-05.

“Alexander has been a great representative of Honda in the IndyCar Series, from his Indy 500 victory in 2016 to competing for the title this past season. We are pleased to have this opportunity to build our relationship with him through our sportscar program.”

Rahal tweeted: "I am bummed to not be joining my friends @Team_Penske for the 2019 @IMSA season, however I simply could not fit properly in the car to perform at my best, therefore I had to step down from my role. I wish them the best, go get that #ARX05 in victory lane!"