Williams' Felipe Massa admitted that if he was in Sebastian Vettel or Daniel Ricciardo's racing boots, "I would be worried".
It follows a disastrous opening test for the reigning four-time world champions, where even the late-to-arrive backmarker Marussia actually collected more mileage.
Italy's Autosprint published a table of mileage after the first winter test of the pre-season, and it makes worrying reading for the Milton Keynes team.
"There are always some problems that are public, or less obvious, sometimes more, sometimes less," he told Spanish reporters at Jerez.
Williams' Felipe Massa, however, admitted that if he was in Sebastian Vettel or Daniel Ricciardo's racing boots, "I would be worried".
"At least they are having some problems this time and are not two seconds faster than the others, as they were in some places last year," the Brazilian is quoted by Totalrace.
Indeed, in a worrying sign of the severity of the problem, Renault's deputy managing director Rob White admitted the cause is "not straightforward" or even fully understood.
"There isn't a single component or system that has caused particular trouble," he admitted.
"The next stage is to identify the root causes for the problems we experienced, to develop the solutions to strengthen our validation process so we can be more confident to tackle Bahrain in a more normal way," he said in a media statement.
Perhaps even more worrying is that the FIA's deadline for initially 'freezing' the specification of the power unit - the end of February - is fast approaching.
Alonso, however, tipped Red Bull and Renault to be ready.
"If this (the events of Jerez) had happened in Australia, it would be more decisive," he is quoted by Italy's La Gazzetta dello Sport.
"I think more than ever this year, we will have to wait for the races to get an idea of where everybody is."