Mercedes has been left "alone" without a key team alliance in formula one.

That is the view of Red Bull official Dr Helmut Marko.

He points out that Ferrari has allied closely with Sauber-Alfa Romeo, while Red Bull is now collaborating more strongly than ever with Toro Rosso.

"Ferrari is the bar at the moment, very clearly," Marko told Auto Bild.

"The car is impressive. How far ahead they are of us is hard to say. But what we can say is that we are clearly ahead of Mercedes."

One reason for that could be that Mercedes has not followed Ferrari and Red Bull's lead by forging a key 'B' team alliance.

"I think Mercedes is a little alone there," Marko confirmed.

"I cannot imagine that the influence Mercedes has on its customer teams Racing Point and Williams is so great," he added.

Referring to the Red Bull alliance, Marko explained: "Toro Rosso did some development work for us with Honda and probably even sacrificed some races for it as well.

"But that makes them stronger in 2019 too. They also benefit from it," he added.