Yamashita suffered a major crash at Suzuka's 130R corner on the opening day of manufacturer testing aboard the Rookie Racing Toyota GR Supra, and had to be taken to hospital.
He was released the following day to begin his rehabilitation, but has not driven a racing car since, missing last week's Suzuka SUPER GT test and this week's Super Formula test at the same track. He will also skip this week's first official pre-season SUPER GT test at Okayama.
However, Yamashita was in attendance on Monday for the opening day of Super Formula action at Suzuka, where Ukyo Sasahara is taking place aboard the #3 Kondo Racing car.
Revealing that he suffered a compression fracture in his lower back from his crash, Yamashita said that he hopes to take up his regular seat at Rookie Racing for the opening round of the Super Taikyu series on March 18-19.
"My back hurts when I drop something and I have to pick it up, but basically there's no problem in my daily life," Yamashita told Motorsport.com's Japanese edition. "For now I haven't sat in a race seat, or even in the simulator. It still feels like it will hurt if I do that.
"I'm thinking about when to come back. Super Taikyu has its first race [at Suzuka] next week and I'm thinking I would like to drive. The week after is the Fuji SUPER GT test, and I hope to drive there as well."
Yamashita sitting out the Suzuka Super Formula test, as well as the shakedown sessions held during last weekend's Fan Thanks Day event, means he has missed his only chances to sample the championship's new SF23 car before the opening round of the season at Fuji next month.
But the 27-year-old says he has been able to learn a lot simply from observing the pre-season action both in person and virtually.
"I wasn't able to come [for the Fan Thanks Day], so I was watching on the 'SF go' [official Super Formula] app," he said. "Just by watching the on-boards and so on, you can understand a lot of things.
"I was able to understand the general atmosphere by listening to Ukyo and Kazuto [Kotaka]'s team radio."
On whether he feels the new SF23 will suit him, Yamashita replied: "If I had to state a preference, I would say I like a car with a strong front end.
"By looking at it, it seems that the front downforce is stronger, because there is a lot of oversteer. Personally I prefer that to a car that doesn't turn well."
