Jose Antonio Rueda collided with the back of the bike of Team CAB Green Power rider Detweiler, 20, during the warm-up lap at the Sepang International Circuit, sending the Swiss rider flying off his bike and landing hard on the asphalt.
The two competitors received treatment on the track and were transported to the hospital by helicopter, delaying the race for more than an hour.
"He has been hospitalized in Kuala Lumpur and will require multiple surgeries. Noah is a true fighter, and the entire CIP Green Power team is behind him," Detweiler's team said on social media on Sunday.
In an interview with the Swiss newspaper Blick, Detweiler's father, Andy, said his son was in stable condition after suffering multiple heart attacks and losing significant blood.
The report added that Detwiler suffered injuries to his spleen and lungs, and the Rueda Red Bull (KTM AGO) team said the Spanish racer suffered a broken hand but was conscious and alert in the hospital.