There have been suggestions that Resta's seat could be in doubt after he failed to finish the last five races in the calendar.
"You have got to take it across the whole season," Fernley told Autosport.
"You have some fantastic results and you have some bad ones and you have just got to balance it all out and make the judgement at the end. You can't take individual results as the way forward."
Force India are yet to confirm either of their drivers for the 2014 season.