Marussia's Technical Chief Pat Symonds believes a top driver would be over half a second per lap faster than both of the team's current rookie drivers Jules Bianchi and Max Chilton.
Symonds, who was technical chief at Renault during Fernando Alonso's championship winning years of 2005-2006 admits having two rookie drivers is not the ideal solution for the back-of-the-grid team.
When asked what the difference would be if someone like Sebastian Vettel or Fernando Alonso was at the team Symonds said: "Of course we would be closer.
"At Renault, we discussed at length Fernando's contribution to the laptime," he told Auto Motor und Sport, "because he is very expensive.
"But our feeling was that Fernando is worth half a second compared to a normal driver.
"Compared to our drivers, it's perhaps a little more than that, simply because they lack experience.
"Our hands are tied," Symonds concluded. "We need to have drivers who also bring money."
Marussia was forced to drop former Toyota driver Timo Glock for this season as the financial situation at the team became serious, replacing him with Ferrari-backed Jules Bianchi and Max Chilton, son of the chairman at insurance company Aon.
Despite Symonds' claims Bianchi is impressing so far this year at Marussia and the cream of Ferrari's young driver academy could be in serious contention for a seat at the Scuderia next year.
Current driver Felipe Massa had looked as if he had overcome the problems that have affected him in recent seasons but crashes and spins at recent races have out his future back in doubt.
The Head of Ferrari's youth academy admitted: "It was very important for Jules to have finally reached the highest level of motor sport," he said.
"This is a key year for him. He has to gain experience and grow as a driver in what is a very competitive environment, learning to manage stress and always stay focused."
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