With the Australian set to leave Red Bull at the end of the season to join Renault, Horner says the number of reliability issues that have been related to the power unit will be of particular frustration for Ricciardo.
"He rode the storm and emerged the other side".
"I think within the team there are secretly some jokes being made about it".
"He was driving a strong grand prix and would have been right there too".
"I think he is becoming more and more rounded in all areas".
Regarding performances this year, Ricciardo now lies in sixth on the driver's leaderboard and just behind his teammate Verstappen.
Ricciardo punched a hole in the wall out of frustration from his early retirement in Austin, which was linked to a failure with the Energy Store component in his engine.
There must be frustrations obviously within him.
While the exact cause of Ricciardo's retirement isn't clear, and may not be entirely down to Renault, the Australian remains undaunted by his decision to switch teams and insists he was always aware that he wasn't jumping straight into a championship challenging auto. "A good and fair fight between Max and Lewis over the last couple of laps gave Kimi [Räikkönen] the breathing space to take a well-deserved win and Max a fantastic second place".
"From a team point of view, all we want to do is finish the year on a high with him and have the chance to celebrate the time he has been with us". But it is a bit unfortunate these things are still happening for him. "He knows the team isn't to blame in any way, we are doing all we can".
"A stunning drive from Max again today starting eighteenth and finishing the first lap in ninth", said Aston Martin Red Bull Racing team principal Horner. "That Ferrari and Mercedes will not be able to run their high power modes, that is what helped us past year".
"We're lacking that horsepower, and this will give us a fairer chance on a Saturday, and you can see we've got a good race auto".More news: Pentagon to send about 800 troops to Mexican border