Williams reserve and development driver Robert Kubica is the latest name to be linked to a possible race seat at Toro Rosso.
Brendon Hartley's position with the team looks increasingly at risk. The Kiwi joined the squad for last year's United States Grand Prix and has now completed ten outings in Formula 1.
Hartley's best result was tenth place in the Azerbaijan Grand Prix. That's the only championship point he's won so far. By contrast, his team mate Pierre Gasly has 18 points and is currently 11th in the drivers standings.
Red Bull motorsports consultant Dr Helmut Marko had previously said that the team had no plans "at the moment" to replace the 28-year-old mid-season. Hartley himself has pointed out that he has a contract in place with the team.
But that appears to have changed, with Marko's latest comments to Speed Week sounding ominous for the Kiwi.
"The situation around Brendon is not pleasing," he said this week. "We will go through this in peace and see what we can do in the future."
Former Red Bull and Toro Rosso driver Daniil Kvyat found himself suddenly out of a job with little warning last year when he fell out of favour with Marko.
Former Sauber drivers Pascal Wehrlein and Antonio Giovinazzi have both been linked with the seat if Hartley gets the push. However Wehrlein is a product of the Mercedes young driver programme and Giovinazzi has been part of the Ferrari Driver Academy.
Formula 2 driver Artem Markelov is at least a Renault development driver. However his recent critical comments of Dr Marko's management style might count against him.
Toro Rosso has also said it is looking to add a Japanese driver to their line-up in the future, as part of their relationship with engine providers Honda.
And now it appears that Kubica might be in the frame for the drive.
France's Auto Hebdo reported that Red Bull might actually prefer to promote Blancpain GT Series driver Jake Dennis or Formula 2 rising star Sean Galael into the race seat. However, neither currently has the superlicense needed for them to take part in a Grand Prix weekend.
Kubica does, and came close to securing a seat at Williams for 2017 before Sergey Sirotkin got the nod instead. But given the team's form so far this season, Kubica might see that as a lucky escape.
Top design and technical chiefs Ed Wood and now Dirk de Beer have departed from Grove in recent weeks. Williams is at the bottom of the constructors standings, and Sirotkin one of only two drivers yet to score points this season.