Daniel Ricciardo admits the stressful process which led to him leaving Red Bull to join Renault for 2019 may have affected his preparation for some of the races leading up to the summer break.

Ricciardo stunned the F1 community in August when he announced his decision to move to Renault, having spent several months weighing up his options in the final year of his Red Bull contract. In the months leading up to August's summer break, Ricciardo and Red Bull's performances dropped off after a brilliant start to the season which saw the Australian driver claim wins in China and Monaco.

That coincided with a time in which he was talking to Mercedes, McLaren and Renault, while also discussing terms of a new deal with Red Bull. It was widely expected he would continue at Red Bull until the Renault move was confirmed in the week following the Hungarian Grand Prix.

Although he insists he was able to switch off all the outside noise every time he jumped in the car for a race, he believes the strain of making that decision had more of an impact on him than he initially realised.

"At time, I didn't think so," Ricciardo told ESPN. "I feel like even if I was to, say, trip and fall over on the way to the car and scratch all my arm, by the time I got in the car it would be blacked out in my head.

Daniel Ricciardo was weighing up his F1 future for the first half of the 2018 season. Mark Thompson/Getty Images

"I guess what would have affect -- which you probably don't think at a time -- is when you're away from the track and instead of getting eight hours sleep a night, you're getting six hours sleep because your brain is ticking... for sure this has some form of an accumulated affect.

"Again, I think I am stronger than that and when I get in the car I am sweet, I am switched on, but maybe it did take a little bit away from me without me knowing.

"For sure there were nights where I didn't sleep as I should have because I had a lot on my mind. Then that builds up and I was probably not as sharp as I once was."

The frustrating run of form continued after the summer break, as Ricciardo suffered the lion's share of Red Bull's reliability issues. He failed to return to the podium after his win in Monte Carlo despite several golden opportunities -- he retired while running strongly in Austin, while suffered a car failure during the Mexican Grand Prix, where he had claimed pole position.

Asked if 2018 was the most difficult season of his career, he said: "One hundred percent. Even if you ignore the results there was so much going on around it.... Highs and lows.

"Some of the DNFs were crazy but then the same year there was the high of Monaco and stuff like that, so it's a weird one. It was definitely as intense a season as I've experienced, both before and after I decided what I was doing next year."