The team will unveil Toro Rosso driver Ricciardo as Mark Webber's successor in the No.2 seat at this weekend's Belgian Grand Prix in Spa, according to German magazine Sport Bild.
"We won't say anything before Spa - that's all I can say," Red Bull advisor Helmut Marko told the publication.
Former world champion Kimi Raikkonen of Lotus, Ferrari's Fernando Alonso and Ricciardo's Toro Rosso teammate had all been linked to the high-profile Red Bull vacancy since Webber announced he was quitting the sport in June.
If the deal goes ahead, the Perth-born racer will follow the path Vettel took in 2009 when he switched from Italy's Toro Rosso to her British-based sister team Red Bull Racing.
But the decision to install a driver without an F1 race win or podium finish could be seen as a risk for Red Bull, who are chasing their fourth consecutive constructor's and driver's championships under the successful driving partnership of Vettel and Webber.
Ricciardo has managed nine top 10 finishes in his 41-race career - a feat which Vettel managed in just 18 events before he was elevated from Toro Rosso, including his maiden grand prix victory at age 21.
Ricciardo's best finish to date is seventh, achieved at this year's Chinese Grand Prix, but Red Bull have shown plenty of faith in the 24-year-old.
Owner Dietrich Mateschitz praised the Perth-born racer after his strong showing at the young driver test at Silverstone last month.
Ricciardo has been sponsored by Red Bull since 2008, when he won the Formula Renault 2.0 West European championship.
With 10 races gone in the 2013 season, Vettel leads the world drivers' championship table with 172 points head of second-placed Raikkonen on 134.
Webber sits in fifth spot, ahead of Ricciardo in 14th.