Horner believes that a torrid run of bad luck has been the big problem for the German, who has not won a race yet in the current campaign, but he insists that the four-time champion's attitude will not change.
"Sebastian has not given up hope on anything," Horner is quoted as saying by The Mirror. "He is still very much focused. He has had a horrible start to the year.
"Everything that could go wrong has gone wrong for him. All the bad luck that could have had over the past five years has come in one period of time.
"Let's see how the second half of the year goes. But his confidence is still high and he's still very, very motivated to defend his title."