The 20-year-old Spaniard will head into Sunday's Australian Grand Prix with a 43-point lead over Jorge Lorenzo of Yamaha and will clinch the championship if he outscores his compatriot by seven points.
"The championship is his to give up at the moment - although the likelihood of that is very, very remote," Doohan told The AAP. "Marquez really needs to have some sort of mechanical problem or some other mishap for Lorenzo to have any chance going forward from here.
"Marquez has been very, very consistent. If he doesn't win, he's generally on the next step of the podium and he only really needs to be in the top three or four to win the championship this weekend.
"He knows he just needs to keep it together. The pressure is really to not do anything too crazy."
If Marquez wins the title at Phillip Island, then he will become the youngest ever MotoGP world champion.