Red Bull have promoted Alexander Albon to drive alongside Max Verstappen, with Pierre Gasly returning to sister team Toro Rosso.
Gasly is currently sixth in the Formula 1® drivers' standings, three places and 118 points behind Verstappen.
Red Bull team boss Christian Horner had claimed the team would keep Gasly in the seat until the end of the season, but the Frenchman has now been demoted back to Toro Rosso.
Albon will now be Verstappen's colleague from the Belgian Grand Prix as Red Bull look to assess their options ahead of 2020.
A team statement read: "Red Bull are in the unique position of having four talented Formula One drivers under contract who can be rotated between the team and Toro Rosso.
"The team will use the next nine races to evaluate Alex’s performance in order to make an informed decision as to who will drive alongside Max in 2020.
"Everyone looks forward to welcoming Alex and supporting him during the next phase of his F1® career."
— Aston Martin Red Bull Racing (@redbullracing) August 12, 2019
Red Bull performed a similar switch of drivers in 2016, with Verstappen handed his opportunity when Daniil Kvyat was sent back to Toro Rosso four races into the season.
Albon has just 12 F1® races under his belt, with the 23-year-old having claimed 16 points and a best finish of sixth, which came at the German Grand Prix in July.