Ricciardo was third and fifth fastest in the two Friday sessions in Melbourne, ending practice two more than a second down on pacesetter Lewis Hamilton's best time.
But Ricciardo insisted that Mercedes is not as far ahead as it appears, and is confident he and team-mate Max Verstappen will be closer to its pace later in the weekend as Red Bull's set-up experiments did not pay off on Friday.
"We made some changes [that] probably didn't work out the way Max and myself wanted or expected," said Ricciardo.
"I don't think they're [Mercedes] insanely quick; sure, they are quicker than us at the moment.
"[But] I feel we can still reel some of that advantage in that they've got."
Ricciardo is hopeful that if Red Bull can improve the set-up for Saturday, it could be in a battle for second-best behind Hamilton that might include new Mercedes driver Valtteri Bottas.
Read the full article on eurosport.co.uk: Ricciardo: Red Bull can 'reel in' Mercedes