The German has won the last three races, partly thanks to improvements made to the Red Bull car, while Alonso's form has dipped.
"[Red Bull] do it every year, so it's not a surprise that it's happened again," he told the Sunday Express.
"Every year, Red Bull give Sebastian an incredible car. Whilst they have struggled in qualifying this year, generally their race car has been great all season.
"They've take another step and I don't think anyone can keep up with them at the moment. Sebastian is a big favourite [for the title] now."
There are four races remaining this season, including today's Grand Prix in India.