Sauber are hoping to finalise their 2019 driver line up in the coming days with Marcus Ericsson and Antonio Giovinazzi in contention.
Earlier this month Sauber announced Kimi Raikkonen would return to the team next season, signing a two-year deal.
The Finn is replacing Ferrari-bound Charles Leclerc.
There was, however, no mention of his team-mate at the time.
While current driver Ericsson is hoping his sponsorship ties keep him in the Sauber seat, Ferrari are reportedly wanting to put junior driver Giovinazzi in the car.
Team boss Fred Vasseur wants to make a decision “soon.”
He said: “The last two weeks for me have been a bit of a rush on the driver market.
“After Singapore we will sit down with all the persons involved in the discussions and we will take a decision quite soon because I think it’s also good for the team to have a clear answer but it will be soon.”
According to reports Ferrari have first dibs on naming Raikkonen’s team-mate as Sauber’s deal with Alfa Romeo gives them the power to put one driver in the car.
They have until mid-October to do so, otherwise the decision falls back on Sauber.