Jenson Button believes McLaren's problems will be "a big shock to the system" of the F1 team.
Despite showing strong pace in the first pre-season test in Barcelona, McLaren has since struggled, initially in Bahrain and so far throughout practice ahead of the Saudi Arabian Grand Prix.
The team had been on an upwards trajectory in recent years, notably finishing in the top four in the constructors' standings in the past two seasons.
On current evidence, however, McLaren appears a long way off extending this run.
"It's a big hit because it feels that at Barcelona testing the car was working," 2009 F1 champion Button told Sky Sports F1.
"I was following the times and they could have been running a little bit less fuel than the others, but not really that much.
"The pace looked good and they seemed reasonably positive about the car but then they go to Bahrain and they're basically nowhere.
"They had a lot less testing. They had their issues, of course, in testing in Bahrain but still, it's a big hit. It's a big shock to the system. "
McLaren problems have 'no quick fix'
With a 23-race schedule this season, McLaren will be hoping it can turn around its fortunes before the points loss to its rivals becomes too great to make up.
Assessing McLaren's problems, former F1 driver Paul di Resta said: "When you look at the concept difference between the top three teams and where McLaren fit in there, it looks like that concept is not massively different.
"It is just how fundamentally you're achieving the downforce and if your tunnel is giving you the feedback you need.
"We know they are making a new wind tunnel, but that isn't going to be working for a little while as well. It's not a quick fix."