SPIELBERG, Austria (REUTERS) - Mercedes boss Toto Wolff said he has not spoken to Max Verstappen about a possible switch to his team amid speculation linking the 21-year-old Red Bull driver to the Formula One champions.

The Dutchman, one of the hottest properties in the sport and on the front row for Sunday's Austrian Grand Prix, has a contract with Red Bull until the end of 2020.

However German publication Auto, Motor und Sport recently quoted Red Bull consultant Helmut Marko expressing concern that Mercedes were lining up a bid for Verstappen if exit clauses were triggered.

"I haven't spoken to Max," said Wolff when asked about Marko's comments.

"I'd like to continue like we've always done it in the past, first to evaluate our current line up and discuss with the drivers and what their views are before really entering into a proper discussion with anybody else."

Lewis Hamilton, on course for a sixth world championship this season, is under contract with Mercedes until the end of 2020.

Team mate Valtteri Bottas, winner of two races this year and 36 points behind Hamilton in the standings, has a one-year deal with an option for 2020.

Mercedes also have highly-rated 22-year-old French driver Esteban Ocon, currently without a seat, on their books.

Wolff told reporters at last week's French Grand Prix that he was optimistic Ocon would be back in a Formula One car next year.

"Putting all that puzzle into place is something I'd like to do over the next few months, over the summer," he said on Saturday.

Verstappen refused to be drawn on any exit clauses in his contract.

Hamilton, sitting alongside the Red Bull driver in the post-qualifying press conference, said it was all news to him.

"I think the team's pretty happy with Valtteri and me," said the Briton.

"I don't mind driving with you," he added to Verstappen. "I'll drive against whoever."