Marquez, an eight-time world champion, finished 10th at his last MotoGP race before undergoing a fourth operation on his right arm.
The Spaniard - who will be out of action for at least the next few months - revealed it was just a case of finishing the race rather than attacking for higher positions.
"Of course, it was a very demanding weekend," Marquez said. "Not only from the physical side, where every weekend I suffer a lot but especially the mental side. It was very difficult to keep concentration.
"I received the news (about the operation) on Friday, but if I received that news on a Wednesday or Thursday, I would not race here. But I was here, Honda allowed me to choose and I decide to continue the weekend.
"I said, 'Okay, I will continue racing. I will take a risk because you're riding 350 ks per hour. But I will work for [Honda and the team] to give my input for the future.
"It was a difficult race. I enjoyed 6-7 laps in the beginning, I did a great start and I saw the front group. And I was able to ride more or less in the same pace. But then I had one warning and I gave up because already I started to get arm pump, with a lot of pain and a lack of power.
"Today it was important not to make crazy things. In the end I didn't try to attack Oliveira, just finished the race."
"It's an operation and everything can happen," added Marquez. "You never know. But it's the correct decision because riding like this, I cannot continue.
"Of course you are always worried about a fourth operation in the same arm. It's not easy. But when they called me on Friday, gave me the results and told me all the information. I breathed (a sigh of relief).
"Because there was the possibility to get the results and they might say 'okay, the rotation is not so big, up to you…' Then, woah, it's a big decision.
"But they called me and said straight away: 'Come next week. We don't know how you are doing what you are doing now. But this rotation is too big. And you must stop now'.
"So for me it was an easy decision. Friday was one of the best days of the year."
The Honda driver says it is the "correct decision" to have an operation on his arm but said the injury he has sustained will have a huge impact on not only his career but for the rest of his life.
"Having the operation is the correct decision for my future, but it's not like I'll have the operation and (automatically) win again. No.
"The target of the operation is to try to enjoy riding again and have a normal life again. Forget the painkillers and all these things. This is the target of the operation.
"Then if you have all these things, and you enjoy it again, the possibilities of good results will increase."