The Italian was ruled out of the last two rounds of the championship after contact with Luca Marini in the Sprint race at Portimao in Portugal, which left him with a fractured right shoulder.
Still not fully fit, Bastianini does not believe he will be in a position to fight for race victories until Mugello hosts Round 6 of the series from June 9-11, with Le Mans in France (May 12-14) taking place before then.
“I'm very happy to be here again,” said Bastianini, who returned to the track last Monday in Misano on a Panigale V4S to assess his condition.
“It's difficult to watch the Grand Prix from home so now it is better. I had given 100 per cent to try to be physically ready for Austin, working out in the gym and continuing physical therapy, but the doctors advised me to wait.
“Monday I was back on my bike with the Panigale and my feeling was quite good, but not very well. I know the situation,” he added.
“I'm not 100 per cent but it's important for me to try and bring the confidence back with the bike.
“I'm not here to win in this event but I have to try and do my 100 per cent. Jerez is a track I like, but I still know I am not at 100 per cent of my strength, so this GP will be like a test for me to get back in shape for the next races.
“I want to arrive in Mugello at 99 percent. This can be possible. From that race my championship will start.
“Now, I'm not in the position to be strongest for all of the race but maybe in Mugello.”
Bastianini won four races in 2022 and is tipped as a title contender this season on the Lenovo Ducati. His chances still remain alive, with team-mate and reigning champion Francesco Bagnaia throwing away valuable points after making two unforced errors in Argentina and America.