Bayern strengthened their squad by signing Philippe Coutinho on a season-long loan from Barcelona – and the Brazilian scored his first goal in Saturday's 4-0 triumph over Cologne.
Van Buyten, though, has warned his old club not to rely too much from Coutinho's individual talent if they want to fight on multiple fronts this season.
"For me, it is always a work of the whole team. You have top players like [Robert] Lewandowski and many others, but you can't think that if you hire a player like Coutinho, he has this magic wand to do something special," Van Buyten told Omnisport.
"I think it's teamwork and you have to get a top performance every time. No matter which team you have to play on the weekend, it's always the same process. If you ever think that it's easy, it's a negative process.
"It's about your mentality and from my time back then, I know very well that we had a lot of players as far as the character was concerned, they were very concentrated and really had the focus in their heads to win the championship, and also to go far in the Champions League.
"They're all top teams [in the Champions League] and it's not easy to make your way there. Bayern already needs a team at the top level."
Van Buyten also believes Borussia Dortmund still must prove they can stay the course in a potential Bundesliga title race, despite strengthening their squad.
After a busy close season that included the return of Mats Hummels from Bayern, Dortmund are tipped to push the reigning champions all the way in the 2019-20 season.
Thorgan Hazard, Julian Brandt and Nico Schulz have also arrived to bolster Lucien Favre's options, with Van Buyten impressed by the way they performed in the 0-0 Champions League draw against Barcelona last week.
However, while he expects them to challenge Bayern once again after finishing second in the previous campaign, the Belgian needs to see if BVB have the depth required to cope when their resources are stretched.
"Borussia Dortmund made very good transfers and they are a good team on the pitch," he said.
"They will definitely be a team that will fight for the championship in the Bundesliga until the end. But there are still one or two other teams that will also play for the title.
"Against Barcelona they [Dortmund] have also shown in the Champions League that they can play good games there – but they have to show that in Barcelona as well.
"As I said, things are looking good at the moment, but you have to see how things go from there.
"If there are injuries or illnesses, then you have to show that the squad is there and that the other players can also be successful."