The Australian has come under pressure in recent races as he continues to be overshadowed by his McLaren team-mate, Lando Norris.
After a tough 2021 campaign, during which he struggled to adapted to the MCL35M, it was hoped fresh start afforded to drivers by new regulations would see him back on an even keel.
In the seven races thus far in 2022, however, Ricciardo has only finished ahead of Norris once when the pair have both seen the chequered flag.
“It's not going well, and as Daniel rightly points out, nobody puts more pressure on him than he puts on himself,” Brundle told Speedcafe.com.
“He's a world class sportsman, and a world class racing driver. He's won eight races, 32 podiums, he's 32…
“Form is temporary and class is permanent, as they say, and I don't think he's forgotten how to drive a Formula 1 car.
“Something's not working and I don't think it's just about the 2022 cars because if you take Monza out of last year, it wasn't tremendous either – Monza was a bit of a saviour.”
While pressure has been gathering steam for some time, it came to a head leading up to the Monaco Grand Prix two weeks ago.
Then, McLaren Racing CEO Zak Brown suggested the team's relationship with Ricciardo hadn't lived up to expectations.
However that wasn't a universally accepted line from the organisation, with team principal Andreas Seidl, who oversees the operation day-to-day, threw his support behind his under-fire driver.
Some of the woes Ricciardo's experienced, at least on Sundays, during 2022 can be easily understood.
Bahrain, for instance, was his first race back following a bout of coronavirus, having also sat out the final three days of pre-season testing.
In Saudi Arabia, the car failed him, while in Australia he had his best performance of the season and was glued to the rear wing of Norris.
Miami proved a circuit that played to the weaknesses of the MCL36, with Ricciardo the only McLaren driver to see the flag.
A fault was then found on his car following the Spanish Grand Prix which explained why he could do no better than 12th in a race Norris finished eighth.
In Monaco, a practice crash the team has since taken responsibility for left the Australian on the back foot.
Given the torrid start to the year, some of which has been if his own making and some not, it's easy to understand the criticism he's faced.
However, it also suggests that Seidl's defence is warranted, even if Norris has tended to be the better performing of McLaren's drivers.
“I don't think it's just about Lando going extremely well,” Brundle opined.
“I think Daniel's not performing at his potential for whatever reason.
“Lando is going well, but Daniel's better than his results look.
“It's odd,” he continued.
“McLaren want it to work, Daniel wants it to work.
“Teams love continuity, it's a great driver pairing, truly great driver pairing, they work well together on all levels – I'm sure technically, you know, driving, on the marketing and side, all of that.
“So I think both parties really want it to work well, so it's a bit confusing.
“Wherever Daniel's speed's gone to, he needs to get it back.”
While there is no obvious candidate to replace Ricciardo should the partnership deteriorate further, Brundle warns against complacency.
McLaren has signed IndyCar driver Colton Herta for a test programme this year and has Pato O'Ward on its books too.
While neither currently look race ready for F1, there is no reason why, with enough investment from McLaren, that either couldn't be rushed into action should they so choose.
There are others too.
Pierre Gasly has shone at Scuderia AlphaTauri and has recently been overlooked again for the senior Red Bull team, while Oscar Piastri is both highly rated and technically available, albeit with a link to Alpine.
“It's a tough business we're in,” Brundle pointed out.
“There's 20 Formula 1 drivers in the world, and McLaren can't go into 2023 if Daniel's performing at this level with him.
“I think that's what they're saying, and I can imagine them sitting down and talking about it.
“I'm a huge fan of his as a driver, as a person, as an asset to Formula 1. We'll all be ecstatic if it all starts coming together and it settles down.
“It's a head game, like sport at the highest level anywhere and everywhere,” he added.
“He's got to get his head back in the right place.”
Ricciardo is next in action at the Azerbaijan Grand Prix this weekend, Free Practice 1 for which takes place from 21:00 AEST on Friday.
Sunday's race is set to commence at the same time with the action live on Kayo.