Sauber has decided against using Ferrari's latest updated engine this season because of the knock-on impact it would have on other aspects of car design.
The Hinwil-based team had evaluated using Ferrari's latest specification engine for the final races of the season in a bid to lift its performance.
But having looked into the extra work needed to accommodate the different cooling needs of the update, Sauber believes it is better to stick to the same iteration it has had all season than make car modifications.
Team principal Monisha Kaltenborn said: "It wouldn't have been the right step with our car because we could have had certain issues there, and we didn't want to take that risk."
Kaltenborn made it clear that there was no issue with Ferrari holding back on making the update available to customers.
"It had nothing to do with the agreement," she added. "It is a question of whatever strategy we decide with them for different reasons – and what is possible on our car and what is not."