The nine-time world champion suffered a double fracture in an accident while riding an off-road enduro bike on August 31.
Italian great Valentino Rossi has not ruled out a return to MotoGP in Spain this weekend, three weeks after breaking his right leg, after getting back on a bike for some test laps on Monday.
Yamaha said the 38-year-old, whose doctors had advised a 30-40 day recovery period, had ridden around the Misano circuit near his home in eastern Italy on a YZF-R1M road bike to "put his fitness level to the test".
The evaluation was inconclusive after rain forced him to cut the session short, however.
"He will decide by the end of Wednesday... whether he will attempt to take part in this weekend's Gran Premio Movistar de Aragon," Yamaha said.
Motorsport.com quoted his father Graziano as saying Rossi had completed seven or eight laps and hopes to test again on Tuesday.
"I was told he felt a lot of pain in his right leg, but he could not determine in so few laps whether a return at Aragon could be possible," he said.
Rossi, a nine-times world champion, suffered a double fracture in an accident while riding an off-road enduro bike on August 31.
He missed the San Marino Grand Prix at Misano and Yamaha said last week that Dutch Superbike rider Michael van der Mark would replace him at Aragon on September 24.
The Italian is fourth overall and 42 points adrift of Honda's Marc Marquez and Ducati's Andrea Dovizioso, who are tied at the top of the championship.
The race at the Motorland Aragon circuit is the 14th round of the 18 race season.
Yamaha team boss Lin Jarvis said last week he doubted Rossi would go there unless he feels he could be fighting for the top five or six positions.
In 2010, Rossi broke his right leg in practice for the Italian Grand Prix, and returned to MotoGP after an absence of six weeks.
