Kimi Raikkonen is expected to stay on the Hinwil team while Mick Schumacher is keen to take second place from Ferrari, currently occupied by Antonio Giovinazzi.
Schumacher was due to drive in FP1 at the Nürburgring on Friday, but bad weather meant he was denied the opportunity.
While no alternative slot is planned, Vasseur still expects a decision to be made sooner rather than later.
“I think it was last Friday when I told you it would be for the next few weeks,” he said.
“I think we’ll have to make a decision later this October to be relaxed about the last four events.”
Regarding the lost Friday session, he said: “It’s a shame and for everyone, especially Mick.
“He was very dedicated, he was at the factory last week, he worked very hard with the engineers, he prepared well for FP1 and then what happened happened.
“Sure it’s a shame. But I think at least he took some of the preparation.”
Vasseur admitted that putting Schumacher in the car for another FP1 won’t be easy, especially given the new circuits ahead and the need for Giovinazzi to earn miles.
“It’s not that easy because in Portimao everyone has to learn the track and it’s not the best place to give FP1 and then Imola is without FP1.
“Then we have to go to Istanbul. We have to sit down and have a discussion with Antonio, but it’s not the easiest thing now, I think. And he has the two events in Bahrain that he drives in F2.”
Vasseur added that every test trip is not about the ultimate lap time, but rather about assessing the driver as he works on the team and with the engineers.
“When a driver gives the FP1 to someone else, the first step is to avoid accidents and damage the FP2, so we ask them to be a little calm.
“And then you can’t judge them by the lap time, that would be unfair.
“But it’s more about the approach, the way they accelerate the pace during the first RP, and the feedback they can give the team.
“Because when you talk about pace, you have to trust what he’s doing in F2 more than the 10 laps he’s doing in FP1.
“As a team, this is the only way to gauge the attitude, relationship he has built with the team, and technical feedback.”
