O’Neill joined Haas late in 2014, tasked with setting up the team to join the F1 grid in 2016 and assuming responsibility for the day-to-day operational management of the track staff.

It came after he was drafted in to set up Marussia, which later became Manor, for its 2010 debut and assumed the role of team manager.

Previously, he spent seven years at Jordan, fulfilling the roles of team manager and chief mechanic, followed by a short stint in A1GP.

O’Neill will leave the team after the upcoming Italian Grand Prix to take up a role with DKR Technologies, working alongside former Red Bull chief mechanic Kenny Handkammer.

He will be replaced at the American outfit by Simmonds, whose final race with Renault is believed to be the Japanese Grand Prix.

Speaking at Spa on Friday, Steiner said of O'Neill: "He’s leaving. He’s not here, he’s coming to a few more races.

"David is leaving for family reasons, he relocated to the United States. That doesn’t work for us. He will be around for a few more races and then he will be gone.

"I don’t know any detail about his company but he is free to do that. We have a good relationship. He helped a lot bringing us to where we are."

Renault chief Cyril Abiteboul said: “I can confirm that [Simmonds has left]. We may or may not be making an announcement in relation to him.

“Geoff is an important person of Enstone. Not just Renault and Lotus but Benetton before.

“Geoff has been part of the Enstone family so we have to prepare a big farewell party, even though he may or may not be going very far. But I can confirm this first part of the move at least.”