Lotus Renault driver Kimi Raikkonen and Toro Rosso duo Daniel Ricciardo and Jean-Eric Vergne have all been shortlisted for the role next season, but Horner insisted that they would consider their options before making a decision.
Horner told Sky Sports News: "We want the fastest lineup that we can and Kimi's obviously an attractive option.
"The youngsters are attractive as well. We want to take our time and evaluate the options but the reality is that it's probably between those three."
Webber is leaving Red Bull after seven years with the team.