Robert Doornbos has decided to leave the Newman Haas Lanigan Racing team with immediate effect, he announced on Tuesday.
The Dutchman has raced for the team since the start of the season, and is currently in 15th position in the championship.
The former Formula 1 driver is also leading the Rookie of the Year standings.
Doornbos said he had decided to take up an option to leave the team, but claimed he is planning to stay in IndyCar.
"We had the option to leave the team after 12 races which I made use of," Doornbos wrote on his website. "I want to stay in IndyCar Series and I will announce my future plans very soon.
"I like to thank the team and especially Mike Lanigan and Carl Haas. I wish them a bright future."
Dutch press has linked Doornbos with a move to the HVM team.