The factory Ducati rider leads Pramac's Jorge Martin by 21 points in the championship coming into the finale in Valencia.
But his weekend got off to the worst possible start, as Bagnaia struggled to 15th in practice and missed the Q2 cut while Martin sailed through in second.
Bagnaia says he was losing half a second in just three corners due to issues getting his Ducati stopped, but thinks it is "fantastic" that this is the case, rather than that time loss being across the whole lap.
"I was struggling. It was not an easy day from the start," Bagnaia began. "I struggled a bit with brakes at the start of FP1 and then we put in something different and I was feeling OK.
"But my feeling today was not the best on the entry of the corners. I was always having a lot of locking and losing a lot of feeling.
"But honestly, checking the data after the time attack, I lost five tenths in three corners. So, it's easier to understand where to improve like this, but five tenths in three corners is a huge amount of time.
"We will improve for tomorrow. For sure, normally we have time and we finish the job on Friday already. And this time we need more, so tomorrow morning will be a very important session."
Source: Autosport