Coulthard was McLaren's longest-serving F1 driver, starting 150 grands prix for the team from 1996-2004.

"The issues they have with the Honda power unit are just so big," Coulthard told Motorsport.com during an event to promote Channel 4's F1 television coverage.

"They have reliability issues and a lack of horsepower - they don't really go hand in hand with development.

"They'll improve but they're so far away it would be Houdini-like if they were able to come back and genuinely be competitive this year just because the pace of the racing season."

The 13-time GP winner questioned whether Honda had a long-term future in F1 given its poor performance since returning in 2015.

McLaren is already known to have sounded out Mercedes about a supply of engines.

"McLaren will [stick around], but whether Honda do or not is another question," he added. "They've made the commitment, it's cost them a lot of money, they're on the global stage but they're not on the stage to fail. At the moment, that's what they're doing."

The McLaren MCL32 hit serious reliability issues throughout pre-season testing at Barcelona, completing under half of the amount of laps run by benchmark Mercedes.

At the front of the field, Coulthard expects Mercedes to face a threat from Ferrari this season but that there will be little chance of upsets from teams further back.

"I'm hopeful that Ferrari's performance in winter testing will translate to strong performances during the grands prix," he said. "Your three teams to easily pick out, of course, are Mercedes, Ferrari and Red Bull.

"It's difficult to imagine how a Williams or any other team can seriously challenge the frontrunners and the team who continue to underperform is McLaren."

Samarth Kanal