The team said in an update on Monday that the double world champion was making a solid recovery in hospital in Barcelona, chatting to family and friends, and would remain there under observation.
They cast doubt, however, on whether the Spaniard would take part in this week's final four-day test in Barcelona before the opening race of the season in Australia on March 15.
McLaren said a detailed analysis of damage to the car, and telemetry data, indicated "the accident was caused by the unpredictably gusty winds at that part of the circuit at that time, and which had affected other drivers similarly.
"We can categorically state that there is no evidence that indicates that Fernando’s car suffered mechanical failure of any kind," they said.
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The data also showed the car had no loss of aerodynamic pressure nor was there any electrical discharge or irregularity in the ERS (energy recovery) system before, during or after the incident.
"That last point refutes the erroneous rumours that have spread recently to the effect that Fernando was rendered unconscious by an electrical fault. That is simply not true," the team said.
"Our data clearly shows that he was downshifting while applying full brake pressure right up to the moment of the first impact -- something that clearly would not have been possible had he been unconscious at the time."
While the driver's manager posted a photograph on Twitter of a smiling Alonso giving a thumbs up to the camera, McLaren said he would need time to recover from sedation.
"We intend to give him every opportunity to make a rapid and complete recovery, and will evaluate in due course whether or not he will participate in the next Barcelona test," they said
The third and final pre-season test starts on Thursday and ends on Sunday, with the teams then returning to their factories before flying to Melbourne.
Alonso is back at McLaren, where he spent a sole season in 2007, after five years at Ferrari to start a new Honda-powered era for the team.
Testing had been challenging for McLaren even before the accident, with Alonso and 2009 champion team mate Jenson Button having to contend with repeated power unit problems.
(Reporting by Alan Baldwin, editing by Ken Ferris)
