Gasly has often found himself battling midfield teams this year, while former teammate Max Verstappen scored podiums and race wins.
From the Belgian Grand Prix onwards, Verstappen will be paired up with Albon, who receives the promotion despite only having 12 F1 starts under his belt.
"Gasly has problems in traffic, he loses places and he can't overtake," Marko told Auto Bild. "So we had to react and give Albon a chance until the end of the season. Gasly takes his place at Toro Rosso and then we see who will be driving next year next to Max."
The 2019 campaign also marks Red Bull's first with Honda. The partnership has so far been successful, with Max Verstappen taking two wins and three further podiums.
Marko admits that Red Bull underestimated the Japanese manufacturer prior to the start of the season, and believes the Milton Keynes squad can be competitive at any circuit in the second half of the season.
"We built a car with too little downforce," Marko admitted. "We underestimated the progression of our new engine partner Honda.
"They delivered more power than we thought. That's why we first wanted to compensate for the missing power with a chassis that is very aerodynamically efficient, but we corrected that.