Team principal John Booth fears Marussia will not be ready in time for Formula One's season-opening Australian Grand Prix.
Marussia missed the first two days of the opening test in Jerez last month due to technical issues, and then only completed 30 laps, or 132kms, over the final two days.
In the second test in Bahrain last week, the team's gremlins continued to bite, starting off with a computer virus which virtually wiped out the opening day.
Problems with the power unit and fuel system on the third and fourth days at the Sakhir circuit meant, come the conclusion, drivers Max Chilton and Jules Bianchi had managed just 29 laps.
Ahead of the final four-day test that begins in Bahrain on Wednesday before the cars head to Melbourne for the Australian GP from March 13-16, the Banbury-based outfit have chalked up just 288kms so far - less than a Grand Prix race distance.
Speaking to Autosport, a concerned Booth said: "I'd be lying if I said I wasn't worried in the slightest.
"It's okay thinking you can sort the problems, but you have to prove it. But I am very hopeful.
"We have done nothing on set-up whatsoever but, having said that, the drivers report that what they have done, they feel pretty confident with.
"The brakes are fine and we improved that over the week; it has come on in leaps and bounds.
"We have only got a couple of days before the next test then four days of testing and we just have to maximise what we have left."