World number five Draper exited the French Open in the fourth round with a 5-7, 6-3, 6-2, 6-4 defeat against Kazakh Alexander Bublik on Monday, missing out on a potential quarter-final clash with world number one Sinner.
"I'm incredibly disappointed with the result," the 23-year-old Draper told a press conference.
"You know, obviously I'm coming into the clay-court season having barely won any matches on the clay before. I keep that in mind, obviously, but I felt good.
"I felt good coming into this tournament. I felt like my level was building. Then today, it's a really, really tough loss to take for me."
Draper has beaten French Open champion and world number two Alcaraz twice in six encounters and has a 1-1 win-loss record against Sinner but feels he does not belong in the same league.
"I still think I'm a long way behind those boys a little bit. I still have lots to learn," Draper said.
"If you look at how many matches they've played, they've probably played double the amount that I've played. They're probably a year, two years ahead of me.
"I do have a lot to do to catch up with them, in all honesty. My level is getting better all the time, but it's not just the tennis. It's the consistency. Even though I've been more consistent, it's doing it when it matters, and these are the tournaments that matter."
