Gasly failed to make it out of Q1 for the Australian Grand Prix on Saturday as a strategy error cost him in qualifying.
He, according to Horner, drove the “wheels off” his RB15 to chase down a top ten showing on the Sunday only to come up short in P11.
But while Gasly was disappointed not to score, Red Bull are expecting big things from him down the line.
So much so that Horner says the team chose the Frenchman because they believe he has “more potential” than Sainz, the driver who was first in line to replace Daniel Ricciardo.
Red Bull, though, opted for Gasly while Sainz joined McLaren.
“Carlos is a talented driver and I am happy to see him continue his career in F1 with McLaren. But we had the feeling that Pierre had more potential for us,” said team boss Horner to f1only.fr.
“Age does not matter, although it’s true that I feel old, because the age of the two pilots added up does not reach mine, whereas I am one of the youngest team bosses.
“Max [Verstappen] has already demonstrated an excellent level of performance in the second half of the 2018 season, which is a great strength.
“Pierre, meanwhile, has a long way to go, we’ve promoted him after just a year at Toro Rosso, maybe a little earlier than expected, but he has the full support of the team and is very good at a multi-season experience in the junior team.”