That is despite a raft of new technical regulations coming into force that many believe will level the playing field, but Horner feels that Mercedes' engine advantage may still be too much to overcome.
"I think it's going to be tough to overcome Mercedes, they will go into next year as the clear favourites," he told ESPN. "They have won three consecutive world championships, they've won 50-odd Grands Prix in the last three years. We're hopeful with the new regulations, it should balance out the emphasis between chassis and engine. We're confident we should make a bit of progress over the winter with the engine."
However, with Red Bull one of if not the strongest team aerodynamically, Horner feels that if Red Bull emerge from the winter close to Mercedes, they could overhaul them.
"We have been through tight championship battles, in 2010 and 2012, that did go down to the wire. I think that gives you a strong experience to deal with those situations," Horner said. "It will be a new experience for Mercedes, when they do come under pressure, which inevitably will happen at some stage. I just hope it is Red Bull that is able to put them under pressure."
Bahrain International Circuit - Winter testing