Ex-Formula 1 driver Kobayashi enjoyed his strongest qualifying result of the season last weekend with sixth on the grid, and was promoted to fourth by the first-lap crash triggered by Liam Lawson's spin exiting Turn 2.
The KCMG driver was running close behind Ryo Hirakawa when he made the decision to make an early pit stop on lap 11 of 37.
But an agonisingly slow tyre change dropped him out of the podium fight and behind the much slower car of Kazuya Oshima, eventually preventing him from finishing any higher than seventh.
Kobayashi has still yet to win a Super Formula race in 59 attempts, despite having previously finished second place five times, but has not stood on the podium since the 2019 campaign.
Speaking to media post-race, Kobayashi was despondent, insisting he felt he had the pace to win without the pitstop going wrong and hinting his patience with things outside his control repeatedly going wrong has run out.
"The car is getting better this weekend, things were going well, we had the pace," Kobayashi said, looking dispirited.
"When I was following [Tomoki] Nojiri and Hirakawa in the early part of the race, I knew I didn’t need to push so hard. It was easy to follow, and I was managing the tyres and the gap, and I tried to pit earlier than them. Just the pitstop was terrible.
"I work so hard myself, and it’s been a long time that we were struggling and didn’t have the pace, now we come back… I am fighting for the win and they make a mistake in the pitstop.
"Maybe it’s my problem. Even if I make a fast car, work hard… something always happens. I think I shouldn’t be here."
Kobayashi said at the start of the year he was approaching the 2023 season, his ninth in Super Formula, with the intention of walking away from the series if changes to KCMG's team structure failed to bear fruit.
When reminded of those comments, Kobayashi said: "Exactly. I'll do my best [in the final round at Suzuka] as if it's the last time."
Clarifying those remarks, he added: "I'm not sure if I'll race in Super Formula next year. I'm exhausted..."
Kobayashi's admission he could be prepared to leave Super Formula comes a week after he made his NASCAR Cup Series debut with Toyota at the Indianapolis road course.
The 36-year-old is currently combining Super Formula with racing in the World Endurance Championship, but has expressed interest in an expanded programme in NASCAR - including trying his hand at ovals.
Additional reporting by Kenichiro Ebii
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