The now 29-year-old Swiss contested over 50 races for Toro Rosso until 2011, going on to become a top sports car and Formula E driver.
But now with Pierre Gasly moving to Red Bull Racing, and Brendon Hartley having underperformed this season, Buemi is very much back in the running.
He had a seat fitting at Toro Rosso’s Faenza base late last week.
However, team boss Franz Tost told Blick newspaper: “It is not planned that Sebastien will be used by us this year.”
But he also admitted that Buemi is “not commenting right now”.
Dr Helmut Marko, the boss of Red Bull’s F1 programme, admitted that he will meet with Buemi in Singapore this weekend.
“I know that we have recently renewed the contract with Buemi as a simulator driver for another year. In Singapore we also have a meeting with him.
“But on Saturday he has to go back to a Formula E test,” Marko said.
One theory is that the Buemi rumours will pressure the struggling Hartley to either up his game or crumble out of F1 completely.
“All speculation,” Marko insists. “It’s a lot of excitement about nothing.
“Buemi has certainly been a topic, but his contracts with other series and Toyota were unfortunately always in the way of a comeback,” he added.