Stoner won ten races on his way to the title last year, and started this season in perfect fashion with a commanding victory in Qatar three weeks ago.
Lorenzo finished behind the Ducati rider in Qatar and while the Spaniard admits Stoner is currently the man to beat, he thinks the world champion can be defeated.
"He is very strong, he rides a quick bike that only he can take advantage of in that way. But he's not invincible," Lorenzo was quoted as saying by Gazzetta dello Sport.
"Can I beat him? I don't know, I'm ready for everything, for winning just like for finishing tenth. I believe in myself regardless of the result. I feel capable of anything, but I have no expectations."
The two-time 250cc champion added he is not feeling under pressure to perform in his rookie season.
"I have no pressure, I'm a rookie. Maybe Valentino (Rossi) has more, because a second place is useless to him.
"Now I have a great hunger. Maybe he (Rossi) lacks that now. But this doesn't mean he can't win on Sunday."
autosport.com