Liam Lawson's struggling start to 2025, however, forced Horner and his team to take action, with Lawson demoted back to Racing Bulls as Tsunoda made the step up.
Despite now being six grands prix deep into his Red Bull career, Tsunoda is yet to look a significant improvement on his many predecessors, with his best finish having been P9 at the Bahrain Grand Prix.
And, speaking ahead of this weekend's Spanish Grand Prix, Horner revealed that the Japanese driver must improve if he wants to remain a Red Bull driver in 2026.
"Personally, Yuki is a great fit for the team," Horner explained. "He's a good guy who contributes well in the garage.
"But if he wants to be considered for next year, he needs to improve further."
That warning won't be anything Tsunoda didn't already know, particularly given the cut-throat way the team operates its race seat opposite Verstappen, but it has made his situation more stark.
Lawson has done little with Racing Bulls to push for a recall to the senior squad, often being outpaced and outraced by rookie team-mate Isack Hadjar, who may be next in line for promotion.