Red Bull motorsport advisor Helmut Marko has re-ignited speculation that Carlos Sainz could leave junior team Toro Rosso at the end of this season, suggesting he wouldn't be "surprised" if the Spaniard was elsewhere.

The 22-year-old's future appeared settled after the brief spat with team bosses over the Austrian Grand Prix weekend. On the Thursday at Spielberg, he told reporters a fourth year in his current seat was "unlikely" only for Marko and senior team boss Christian Horner to in effect confirm him for 2018 by saying there would be no way Sainz would be let out of his contract.

Since then, speculation has been quiet but the tone did ease a little when Horner later claimed Red Bull would listen to "significant offers" for the driver and now Marko, who is known for his straight talking, has done likewise.

"It's difficult to talk about 100 percent in Formula 1," he told Canal 1 Latin America when asked if Sainz's future with Red Bull was certain.

"I would not be surprised to see him at another team because I know what his contract is," he added, "but only we can make it possible."

Indeed any deal for the highly-rated talent would have to be done with Red Bull rather than the driver but there is one ongoing situation that would seem to open that door.

Last year, Renault was one of the first teams to express an interest in Sainz only to have their approach rebuffed, but with ongoing talks between the French manufacturer, McLaren, Toro Rosso and Honda could see him move to the Enstone team in an agreement that sees Renault end their engine supply contract with Toro Rosso and switch to McLaren.

If that was not the case and McLaren remained with Honda, should Fernando Alonso leave, then his fellow countryman is considered an alternative to replace the double world champion.

The situation is very complex, but for Marko to suggest a Sainz move is not impossible would indicate something is happening behind the scenes.