Ducati stayed on at the track following Sunday's race in San Marino to test two new pieces of kit.
Though Rossi was unimpressed with a new, stiffer chassis, he was pleased with the way the swingarm functioned.
"It was a good day," Rossi said. "Today we tried a different chassis that had a different stiffness, but honestly, I didn't like it a lot.
"It was an improvement in some areas, but we had some new problems in other areas. In the end, it's not a real improvement, so I don't think we'll use it again.
"But the positive thing is that we tried a new swingarm that I liked a lot because it gave me more edge grip and more rear grip under acceleration, and it helps the bike to stay more stable on corner exits.
"So of the two things, one worked. I think we'll use the new swingarm starting in Aragon, so there we'll see what our potential is on another track."