The technical director left the team earlier this season following the sudden death of his wife and although his absence can clearly be felt throughout the team, four-time champion Vettel insists it hasn't held back the team's progress with their car for next year.
"Next year's car project started very early for anyone because it is so different," Vettel told Autosport. "It took a while at the beginning of the year to know exactly what is going to happen for next year.
"It's not just one person, so obviously it wasn't easy for the whole team to digest that James is not there anymore. You can imagine he had one of the key roles and an influence, but it didn't impact much on what was going on behind the scenes in terms of looking forward.
"Back at the factory we had a plan, which we are following for a long time, for what is going on for next year."
Bahrain International Circuit - Winter testing