Alex Albon has made a "great" first impression on his new team boss Christian Horner.

Just 12 races into his F1 career, the former Toro Rosso driver was drafted into Red Bull's senior team to replace struggling Pierre Gasly from Spa.

Red Bull says it will choose between Albon, Gasly and Daniil Kvyat to be Max Verstappen's full-time 2020 teammate.

"Alex left a great impression on me," Horner told the Dutch publication Formule 1 after the race at Spa.

"He gives good feedback and his pace is good too."

However, it was actually a difficult weekend for the British-born Thai driver, after an engine change meant he had to start from the back of the grid.

"From P18 to P5 is a very good start," Horner said.

"In the race he was very mature and didn't do anything silly. Hopefully he can perform well for the whole weekend in Monza."

More generally, it was a difficult event for Red Bull, with Verstappen struggling with a Honda engine problem throughout the weekend.

Horner said: "We tested the Spec 4 engine with Kvyat on Friday and what we saw was encouraging.

"The problem with Max arose because his engine was very aggressive, but we could have fought the Mercedes in the race," he added, referring to Verstappen's early crash.

As for Monza, Horner said: "We will probably use the new engine at Monza, but we're not sure yet. We're discussing that with Honda."