Ricciardo announced the surprise decision earlier this year to call time on his spell with Red Bull to join pitlane rivals Renault.
And next season he will race alongside Nico Hulkenberg in a car which would struggle to compete with his current one.
Daniel Ricciardo will be hoping Renault can bridge the gap to Red Bull and pacesetters Ferrari and Mercedes.
But his compatriot Webber has now revealed his doubts about the switch, will take place at the end of the current campaign.
“We’ll all have to sit back and watch, but the move is under a little bit of heat,” Webber told Australian news agency Fairfax Media.
“It has to work for him. He knows in the short term it’s going to be [a step back].
“He’ll be behind Red Bull next year. He’s banking on the long term there. That’s the concern.”
Former F1 driver Webber admits Ricciardo has time on his side in case things go wrong at Renault though.
“That’s what you’ve got to do sometimes, you’ve got to be one step back, two steps forward,” Webber added.
“He’s got a lot of time left but we all would like to see him in a more competitive situation than he’s going to be in over the next two years.”
Since announcing his move to Renault, Ricciardo has failed to replicate the form which saw him win the Chinese and Monaco Grands Prix.
But he insists he is still fully committed to the Red Bull cause.
“I’m not done yet,” Ricciardo said after the Japanese Grand Prix.
“Honestly, not taking anything away from Max [Verstappen] – for sure he’s fast and he’s been driving well – it’s not necessarily that he [had] bigger balls in that corner or whatever.
“I feel like we kind of got left a bit last year as well. Some qualifying [sessions] I’m like: ‘should’ve done that’ in terms of ‘should have gone up on the front wing six clicks instead of one or two’. It’s kind of been stuff in hindsight.
“I’d like to be more pro-active on some things but more set-up. I feel just a lot of the time we understand it but it’s too late.
“I guess we’re still learning. But obviously he’s been getting on top of it more than I have.”
Ricciardo will be desperate to get points on the board at this weekend’s United States Grand Prix in Texas.