Rossi, who will compete in IndyCar this year with Andretti-Herta Autosport, will combine his drive in the United States with the role at Manor.

The 24-year-old American raced with the team in F1 last year, taking part in five grands prix with a best result of 12th in his home race in Austin.

Rossi was one of the candidates to land a race seat with Manor this year, but he ended up losing out to Indonesian Rio Haryanto.

The Californian will attend 11 grands prix, starting with the Russian GP in May.

"I've invested most of my career in F1 and I'm not one to kick my heels and wait for things to happen, so this is my way of staying sharp and prepared," Rossi said.

"It was disappointing to miss out on a race seat with Manor Racing this year; everyone knows I pushed and worked hard for it. As official reserve driver though, I have a very complimentary dual program at the highest level of motorsport.

"IndyCar Series is the premier category of open-wheel racing in North America and extremely competitive. I also have the privilege of racing with a championship winning team, Andretti Autosport. I'm confident this experience will add to my role as a very important cog in an F1 team's wheel.

"My schedule this year is demanding, but no more than a full time F1 schedule. I will attend 11 Grands Prix, only five of which take place during the IndyCar season, and I am certainly used to the travel demands of the F1 calendar.

"It's great to be back with a team I know and with whom I share a mutual respect and passion for the sport we love."