But the German car manufacturer thinks the reigning champion cannot be written off yet.
Red Bull endured a troubled first pre-season test at Jerez last week, completing just 21 laps over the four days of running.
Its overheating and engine problems have left it needing to undertake some big changes ahead of the second test in Bahrain if it is to avoid a repeat.
Mercedes team chief Toto Wolff told AUTOSPORT that he would never have predicted such woes for Red Bull after its years of dominance.
"Personally I am surprised," he said. "The problems on the first and second day were expected, but finishing the test with almost no mileage is not what I would have expected from Red Bull."
Alarm bells ringing at Red Bull
Despite being taken aback by Red Bull, Wolff has made it clear that he is not expecting the team to be down for long, even though he has no detailed knowledge of what has gone wrong.
"Honestly I don't really know what has happened, I have only read the comments," he said.
"They are a good team with a very determined approach, and they have shown in the past that they were very competitive.
"So I have no doubt that they will eventually solve those problems, whether they are on the engine or on the chassis itself."
Williams chief test and support engineer Rod Nelson reckoned that although Red Bull and Renault's woes appeared serious at Jerez, the complicated nature of F1 machinery meant that a solution could be more straightforward than it appears.
"Renault have got some kind of nightmare going on, but that may be one thing," he explained.
"It could be that the battery might me a bit small or overheating."
Ferrari's Fernando Alonso made it clear his team was not wasting time pondering the Red Bull situation.
"It's not our main focus with what others are doing," he said.
"We have a lot of things going on inside our garage, so we are not looking too much outside.
"They [Red Bull] have done little running so far, but they will put things in place I am sure."
But Felipe Massa reckoned that Red Bull's difficulties could be a boost for its rivals - because it opened up the prospect of different teams winning.
"I think if you don't see the Red Bull winning all the time it can be positive for everybody," he said.
For more about Red Bull's crisis, check out this week's AUTOSPORT magazine, available now.