Valentino Rossi says the Mexico City Formula 1 circuit is too "dangerous" for MotoGP and that racing there next season "is not a good idea".
Mexico emerged last weekend as a strong contender to host a MotoGP event in 2019, a move which would bring the number of races on the calendar up to 20.
But the circuit, which returned to hosting F1 in 2015, has walls in close proximity to the track in several areas, as well as widespread tarmac run-offs that are generally considered less safe for motorcycle racing than gravel traps.
"I am quite desperate," said Rossi, when asked for his thoughts on the proposed Mexico race. "First of all [the calendar will] become 20 races, which means we don't have a life!
"Apart from this, the first problem is that it's a very bad track. I don't like it. It's dangerous, also.
"They have to modify some parts of the track [in order for it to be suitable for MotoGP], but it's very difficult to modify like this.
"For me, a race next year is not a good idea."
No major gains in Brno test
Rossi finished fourth in Sunday's race at Brno after qualifying second, having lacked the pace of Ducati pair Andrea Dovizioso and Jorge Lorenzo as well as Honda's Marc Marquez.
He then finished Monday's post-race test seventh fastest, having declared he had nothing "special" to try as he sampled a new front tyre for Michelin and a revised aerodynamic fairing.
Rossi's main focus was trying to improve Yamaha's long-standing acceleration woes, but he said a small improvement that was found would not be ready for the coming weekend's Austria round.
"We didn't have big things, but we had something small to try for the acceleration," said Rossi.
"We worked [to improve] the first touch of the throttle, also to try and save the tyre for the race.
"We also found something quite positive, but unfortunately it won't be ready for Austria, because we have to put it all together.
"It's a difficult job, very small and precise. Maybe we need more time."