The Australian driver is going up against Kimi Raikkonen for the vacancy alongside Sebastian Vettel, and was recently handed a half-day audition in the RB9 at Silverstone to show what he could do.
Despite running off the track at one point, and being unable to work on the car set-up because of FIA restrictions, Ricciardo delivered some consistent pace in the car.
With Red Bull hoping to make a decision over the summer break, Mateschitz has dropped a firm hint that Ricciardo is now in pole position to take the seat, although he also praised the job done by team-mate Jean-Eric Vergne, who still believes he is contention for the seat.
"There is no decision yet, and it is still under discussion within the team," Mateschitz told Autosport. "It will be announced after Budapest.
"But Ricciardo did an excellent job at Silverstone, and [Jean-Eric] Vergne was very good."
Raikkonen's management has been in discussions with both Lotus and Red Bull chiefs about what opportunities are available for next year.
Sources indicate that Raikkonen is keen to stay at Lotus in 2014, but is seeking guarantees that the outfit has the financial capabilities needed to keep up its push for victories.
That security will almost certainly rest on a major investment deal with Infinity Racing being sorted sooner rather than later, after team owner Gerard Lopez revealed that the situation was not as firm as had been previously indicated.
Lotus has won one race this year, and is one of the favourites for the victory at this weekend's Hungarian Grand Prix
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