Max Verstappen doubts whether Red Bull can challenge Mercedes and Ferrari over the second half of this season.

Red Bull have playing catch up to their rivals for the majority of the season with their only race victory to date coming when Daniel Ricciardo took the chequered flag at the Azerbaijan Grand Prix.

Verstappen's best performance to date this season came when he finished third in China and he doubts whether the Austrian outfit can consistently compete with pace setters Mercedes and Ferrari during the rest of 2017.

"I don't know what to expect for the upcoming races but of course it will be quite tough for us to really compete against them," the 19-year-old said.

The 2017 season is set to return with next week's Belgian Grand Prix and Verstappen believes Mercedes, who have won at Spa in each of the last two years, will be the team to beat.

He added: "I expect in Spa Mercedes will be again very strong because in general their power unit is still the best in the whole field, but it's very close [between Mercedes and Ferrari]."