Italian Bastianini suffered a right shoulder blade fracture in the MotoGP season-opener in Portugal last month and also missed the second round in Argentina.
Ducati said he had a further check-up in Forli after completing a few laps of the Misano circuit on a Panigale V4S superbike.
The clinic confirmed Bastianini would still need a few more weeks to fully recover, Ducati added.
"Enea will therefore continue his rehabilitation with the aim of returning to the track in Jerez and will be replaced in Texas by Michele Pirro."
Pirro last raced at the Circuit of the Americas in 2016 as a stand-in for Danilo Petrucci at Pramac Ducati, finishing eighth. He has raced eight times in the last three seasons with a best result of 11th.
The fourth race of the season is the Spanish Grand Prix in Jerez on April 30.
Honda's six-time MotoGP champion Marc Marquez (30) is also ruled out for Sunday's race in Austin and has been replaced by German test rider Stefan Bradl (33) alongside Spaniard Joan Mir (25), while injured Spaniard Pol Espargaro (31) has been replaced by German rider Jonas Folger (29) at the GasGas Factory Racing Tech3 team.
Bradl's last race in Texas was also in 2016, with Aprilia.
Mir crashed in the Saturday sprint race in Argentina, missing the main grand prix.
"I am ready to get back on the bike in America," he said in a Repsol Honda statement. "I have been able to spend this week at home recovering fully after the fall on Saturday and getting back to training."
Bradl's last race in Texas was also in 2016, with Aprilia.
Mir crashed in the Saturday sprint race in Argentina, missing the main grand prix.
