"I think it was also the Wednesday (before the race)," he admitted to reporters at Monza.
"I was at the factory, working in the simulator and at about lunch I was told that I wouldn't race in Spa.
"I still went there but not to the track. I stayed at the hotel rather than causing problems in the paddock.
"There just would have been a lot of questions but I didn't have an answer as to why I wasn't racing," said Kobayashi.
This time around, while Kobayashi was in Tokyo mere hours ago, it was clear that Lotterer and Roberto Merhi were at the front of the queue for the Monza seat.
Ultimately, Spaniard Merhi did not get a full F1 super license. And Lotterer turned down the chance because he would have had to sit out practice.
Asked on Thursday when he got the call to come to Monza, Kobayashi answered: "Yesterday.
"I was in Tokyo. It was all last-minute."
Kobayashi, known and loved for his fighting spirit, was already not particularly enjoying life at the back of the grid when team owner Tony Fernandes pulled the plug.
"The situation is difficult," the 27-year-old admitted on Thursday.
"First of all I'm interested in racing. I want to race. But what happens in the last couple of weeks is not much about sport. I think it was political decisions.
"We had to negotiate even with lawyers -- definitely it is a difficult situation," said Kobayashi.
"I think the team is in a difficult position.
"When I look at the news, I think everything is pretty obvious. Roberto will drive in the first practice and Andre was not very pleased with it. So they called me."
Asked if he considered joining Lotterer in saying "no", Kobayashi answered: "I have a contract.
"If they say I work on the simulator, I work on the simulator. If they say I stay at home, I stay at home."
Asked if he is happy, Kobayashi said: "Am I happy? No. But there's not much I can do.
"I am trying to maintain good relationships, as far as it is possible. But if they want to survive, maybe they are forced to be in this situation."
It is obvious that Caterham's plan is to show Merhi is up to speed on Friday morning, before his backers step up to the grid for Singapore and beyond.
Kobayashi acknowledged that he and his management are looking ahead to a different future.
"Of course we need to think about other options and see what we can do," he said. "First the top teams have to make their choice and then comes the rest."