Red Bull seem to have less of an advantage over the chasing pack this year than they did in their dominant 2010 and 2011 seasons, ex-Formula One star David Coulthard told RIA Novosti on Thursday.
Thursday saw the third day of the second pre-season testing session in Barcelona.
"It looks like Red Bull are fairly stable, McLaren and Mercedes maybe closer than they were," Coulthard said in Moscow, where he competed in an exhibition ice racing event.
"Ferrari is a bit of an unknown, they've got some headline times but the long runs have not been as good at the moment, but I wouldn't write them off. Let's be patient, another three weeks of tweaking and then we'll find out."
The fastest lap in this week's Barcelona test has been set by Williams driver Pastor Maldonado, but Coulthard said it was more important to look at how the cars performed during race simulations.
"I never paid too much attention when I was racing to direct comparisons on headline lap times, but on the longer runs you can start to build a picture," he said.
Coulthard said that Red Bull, where he ended his career after driving for the team in their first three seasons between 2005 and 2008, had completed a long-term strategy by winning the 2010 and 2011 drivers' and constructors' championships.
"They obviously are very proud of their achievements because they've done the ultimate, which is take on the established manufacturer teams and win.
"The initial goal when I was there was to gain credibility in the paddock and then to build a world championship-winning team, and they've achieved it, so you've got to take your hat off to them."
Meanwhile, the 41-year-old Scot said the first Russian Grand Prix, scheduled for 2014 in the resort town of Sochi, would mark a new stage in F1's development.
"It's been coming and coming for ten years, and now it's almost here. To have a true world championship you've got to be in all the major players, and Russia is such a large player in the global economy that it would be one of those landmark races."
Coulthard retired from F1 in 2008 after 14 years in the sport, in which he won 13 races and finished second in the 2001 championship.
He now races occasionally in Germany's DTM series and commentates on F1 for British television.