Red Bull could quit Formula One because rival manufacturers are too fearful of supplying them with engines, according to their chief technical officer Adrian Newey.
Relations with current supplier Renault have broken down and Red Bull has been unable to find a new partner.
"We're possibly going to be forced out of Formula One, Mercedes and Ferrari have refused to supply us out of fear," Newey was quoted as saying by BBC on Monday.
He said the team would take a decision on whether to race in 2016 "well before" the end of the year "because design and manufacturing lead times are such that you need to know what you're putting in the car".
With Sebastian Vettel driving Newey-designed cars, Red Bull won four successive driver and constructor titles using Renault engines from 2010 to 2013.
But Renault has struggled to be competitive in the new V6 turbo hybrid era ushered in last year, and Newey described the "marriage breakdown" as "terminal".
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