Daniel Ricciardo believes his form during 2018 was likely impacted by the effects of considering his future for next season.

The Australian made an excellent start to the season with two brilliant victories in China and Monaco, however, they would be the only high points as retirements and often lagging behind teammate Max Verstappen saw him finish sixth in the Drivers' Championship.

Now, looking back, Ricciardo thinks his personal situation in the crucial few months leading upto the summer break, a deadline imposed by Red Bull to make his decision for next year, likely disrupted his performance.

"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," he told ESPN.

"I guess what would have affected, 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 effect.

"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."

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Eventually, Ricciardo would make the surprise call to move to Renault, ending a 10-year association with Red Bull but even with that resolved his situation wasn't helped by a torrid 2018 consisting of eight retirements and no podiums except for the two times he stood on the top step.

"Even if you ignore the results there was so much going on around it, highs and lows," he admitted.

"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."