Coulthard has now said that Hamilton may have seen his best days and hinted at a loss of 'magic' in his displays.
"This is not Lewis at his prime," the Scot told Channel 4 after the Abu Dhabi GP.
"This is Lewis in a very frustrating two-year state of underperforming. When he gets a winning car again, it'll be really interesting to see if he can rediscover the old Lewis magic."
Coulthard's former team-mate Mark Webber, however, has blamed the team's failings for Hamilton's poor form.
"The car is a mystery isn't it?" the former Red Bull racer said.
"Like Brazil, nowhere. Mexico, Austin - obviously Lewis got done as the car was a bit low there, technically - but ultimately that race there Hamilton was on fire. This thing is literally on or off, it blowing hot or cold, the drivers up and down.
"They're very little nip and tuck and, when you're nip and tuck, you can actually develop, you can actually start to feed off each other. But when you've got a gulf, it's hard technically on a weekend to execute pulling all the corners together.
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