That is despite the fact the rumour was shot down by other senior personnel in Singapore.
“I assume Daniil Kvyat and Carlos Sainz will finish the season with us,” Toro Rosso chief Franz Tost said in Singapore.
Indeed, Jolyon Palmer is insisting his 2017 contract with Renault be honoured in full, and boss Cyril Abiteboul agreed: “We have an ongoing contract with Jo until the end of the season”.
But Marko, the boss of the Red Bull driver programme, told German television Sky when asked about Sainz’s early switch ahead of the Malaysian grand prix: “Everything is possible.”
Spaniard Sainz himself also suggested the issue is up in the air.
“For the moment, I will be sitting in a Toro Rosso in Malaysia and everything else is speculation,” he said.
Sainz added: “The decisions are made by Red Bull, Renault and others, not by me. I am ready for everything, but my thoughts are about Singapore at the moment.
“I will not close any possibility, but all of these agreements we see this weekend did not involve me so I think I would not be the one who knows first.
“It it happens I am ready even though it would not be an easy change and it would take time to adapt,” he added.
What is clear is that Red Bull is ‘loaning’ Sainz to Renault for a single season only, which the 23-year-old said is “a sign that my (Red Bull) bosses appreciate me”.
But another suggestion in Singapore is that Renault really wanted Red Bull to loan them Daniel Ricciardo.
“I’m not surprised,” said the Australian driver. “I’m good looking and fast.”
When asked about the rumour, Marko said: “I think Renault was a little optimistic about the future. When we are on average two seconds faster, why would he change?”