Christian Horner has played down reports Red Bull is entering a second consecutive season amid early troubles.
Team boss Christian Horner is putting a brave face to reports Red Bull might once again be in trouble.
"It (Jerez) was a test that was much more positive than a year ago," he is quoted by Italy's Autosprint.
"We had some problems, it's true, but they were nothing compared to what we faced in 2014, when either we didn't run or it went up in flames."
Most of the problems last week were reportedly connected to Renault's upgraded turbo V6, and Horner confirmed: "The biggest changes we have are in the power unit.
"Renault has worked hard on this, but there will always be things that can go wrong in testing, that's normal."
Another engine option
Autosprint correspondent Roberto Chinchero, however, claims that the story runs deeper behind closed doors at Renault-powered Red Bull.
F1 engine guru and Mercedes title winner Mario Illien has been drafted in at Red Bull's behest to work on the Renault V6, as has AVL, a renowned Austrian powertrain company.
The report said Illien's upgrades could be ready to try at the final Barcelona test, when "it will be the time to choose between the Renault Sport power unit or Illien's".
Chinchero said bringing in Illien "could be the first step towards the creation of a structure able to produce a complete power unit, putting Red Bull on par with Mercedes and Ferrari as teams producing the entire car".