Rossi finished fifth in Spain despite racing with a broken tibia and fibia.
The Italian came in behind fellow Yamaha rider Maverick Vinales but had hoped for a better finish.
Nevertheless, Rossi competing at all was a feat in itself and it has been revealed how he managed it.
Spanish newspaper Mundo Deportivo claim Rossi used a thumb lever made by firm Brembo on his left handlebar to depress the back brake.
The bake brake is usually activated by pressing down on the right foot pedal.
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But Rossi’s double leg break made that almost impossible to do without extreme pain.
So Rossi used a thumb switch – similar to the one Mick Doohan first used in the 1990s – to compress the brake instead.
What is particularly impressive about the brake change is that Rossi, not only concerned about his injury, would have had to use the thumb brake while also dealing with the clutch in his left hand.
Vinales, Andrea Dovizioso, Jorge Lorenzo and Danilo Petrucci have all used the system in recent months.
For Dovizioso it had nothing to do with an injury but was instead used to try and gain an advantage over competitors.
“The riders use it to avoid the curve skids,” Brembo said.
“We could say that the thumb pump is now used as a kind of traction control: it is driven in the centre of the curve to stay close to the edge, straightening the bike more quickly.
“In addition, with respect to the traditional rear brake, the thumb pump offers greater ergonomics.”