But Palmer believes he still has time to prove himself. The Renault driver says he is performing as well as when he won the GP2 championship, F1's feeder series, back in 2014.
"I feel good because I'm getting better every weekend, and the team can see that," Palmer told Autosport.
"Maybe some of the early races were more difficult, but as a rookie I'm becoming more complete as a driver. In terms of progress, the team are going to make a big step for next year. I want to be here.
"I know if I do the job I'm capable of, the team will believe in me and think I can do the job in the future."
Vasseur was tight-lipped on who would be chosen. "I won't put only Esteban and Stoffel in to the loop - because I think that we have a new generation of drivers who for sure will win the championship in the future," the Renault boss said.
"Our two current drivers are doing a good job. Jolyon is a complete rookie and for a rookie he's improving, while Kevin, as someone who didn't drive last year, he's consistent and has scored points."
There have been no such worries about next season for the other British driver on the grid. Lewis Hamilton has enjoyed a summer break as frenetic as his usual lifestyle, including two stops in the Caribbean, a visit to a tiger sanctuary in Mexico - criticised by animal welfare charities - as well as V Festival last weekend.
Button spent most of his break in the United States, a popular destination for many drivers given their relative anonymity in North America compared to Europe.