The German told reporters he was sad to see the Australian lose his seat at the end of the season after the split was announced on Wednesday.
The move leaves Ricciardo, who beat then-reigning champion Vettel in their first year as Red Bull team mates in 2014, looking for a drive for 2023.
"I think it’s a very, very difficult situation to be in," Vettel, who was left without a drive after losing his Ferrari seat in 2020 before signing for Aston Martin, told reporters at the Belgian Grand Prix.
"I had the pleasure to race against him and the not so pleasurable side of getting beaten by him years ago.
"I don’t know the details, but I guess McLaren failed to extract the potential that he has.
"I’m sure that ultimately the talent he has and the qualities he has will shine through."
Ricciardo earned McLaren their first win since 2012 at last year’s Italian Grand Prix, a one-two with team mate Lando Norris.
The eight-times grand prix winner, who has twice finished third in the overall standings, has largely struggled for results since moving from Renault (now Alpine) at the end of 2020.
He has also been outpaced by his younger team mate, who has a long-term deal.
McLaren, who are widely expected to replace Ricciardo with rookie compatriot Oscar Piastri, have failed to produce a car capable of consistently fighting at the front.
Mercedes seven-times world champion Lewis Hamilton also showed support for Ricciardo.
"Really unfortunate for Daniel," said the Briton. "I still think he deserves a place here in the sport so I really hope there’s somewhere great for him because he’s still got lots to achieve."
