Force India believes Nico Hulkenberg will miss the chance to realise the team's potential after leaving to join Sauber for 2013.
The German driver confirmed in October that he will race with Sauber next season after two years with the Silverstone-based squad.
Force India finished behind Sauber in this year's standings, but it outscored the Swiss squad in the final part of the year.
Deputy team boss Bob Fernley reckons Hulkenberg's departure comes at an inopportune moment for the German given the team's form over the season run-in.
"I think so," Fernley told AUTOSPORT when asked if Hulkenberg would miss Force India's potential.
"If you look at the stats since the summer break, the Force India car was clearly the fifth best performing.
"We're still quite a distance off the top four, but since the summer break we've forged ahead of all the others."
Fernley admitted, however, that Force India was sorry to see the German driver leave.
"We're very sad to see Nico go," he said. "He's been a great asset to the team. We've enjoyed having him around and it's a loss to us. There's no question that we're sad he's leaving."
Force India will keep Paul di Resta for 2013, with the Scot's partner yet to be named.
Di Resta struggled to match the performance of Hulkenberg in the second half of the season, but Fernley denied the reason for that was that he was focused on trying to secure a drive elsewhere.
"No, I don't think so," Fernley added. "Up to Singapore, Paul had dominated and Nico was feeling down. Since Singapore it went the other way around. That's how it's gone with them all season, they're so close.
"It's hard to judge. You get those runs. He's just got to dust himself down and get ready for the new season."
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