Although Cosworth has not ruled out supplying a turbo V6 for the all-new 2014 regulations, Marussia is now the British company's only customer for the existing V8.
And most paddock experts expect only Mercedes, Renault and Ferrari to supply V6s next year.
"My understanding is that Cosworth won't be making a 2014 engine," Lowdon explained at the FOTA Fans' Forum in Barcelona.
"I don't work for Cosworth, but that is my understanding."
With Renault currently supplying four teams, and looking set to add Toro Rosso to its roster next year, representatives of the French marque this week ruled out supplying six teams in 2014.
Currently, Mercedes (McLaren and Force India) and Ferrari (Sauber and Toro Rosso) have two engine customers apiece.