Luis Suarez fits like a glove and even Lionel Messi and former star Antoine Griezmann would face competition for places at high-flying Atletico Madrid, says Koke.
From six La Liga appearances, Suarez has five goals and one assist for his new club, while he has created four chances for his team-mates and hit the target with eight of his 22 shots at goal, including blocked shots.
It is form that has helped unbeaten Atleti to third in the table with two games in hand on the two sides above them in the table, and they will face Barca at home after the international break.
Atleti midfielder Koke says Suarez's arrival has allowed others in the team, such as Joao Felix, Angel Correa and Marcos Llorente, to flourish.
"A radical change has hit us in [our] game," he told Cadena Ser. "[Having Suarez] leaves Joao, Correa and Llorente free in some situations. He has fit us like a glove."
One player Suarez has had limited playing time with is Diego Costa, with his fellow Atleti forward out with a left thigh injury sustained last month.
Asked about that link-up, Koke added: "They are two great forwards and they have to adapt together. The team is playing well and has more solutions in attack."
While Atleti's current attacking crop are flourishing, Griezmann – who departed for Camp Nou ahead of the 2019-20 campaign – has struggled to find his best form for Barca.
In seven top-flight appearances this season, Griezmann has two goals and an assist and created four chances, while he missed a penalty in the 5-2 win over Real Betis last week.
The last time Barca faced Atleti in June, it took until the 90th minute for Griezmann to enter the fray despite the game being locked at 2-2 – something that took Koke by surprise.
"I was very surprised to see a player of the stature of Griezmann [not play until] the 90th minute in the last game in which we faced Barca," Koke said.
But when asked about the potential for a Griezmann return, Koke added: "I think now he would have a lot of competition here."
Indeed, such is the strength of Atleti's forward line, Koke believes even superstar Messi – who himself failed to engineer a move away from Barca in a long-running saga during the close season – would find it difficult to get into the team.
"He would also have a lot of competition at Atleti," Koke added.
Koke is particularly delighted to see Llorente beginning to flourish at Atleti, with the 25-year-old excelling in a more advanced role, scoring three goals and assisting two more this term.
"He does everything. He is at a spectacular level. The work pays off and he works [hard]," Koke said.
"I'm happy for him because at first he didn't have a good time by not playing, but all work has its reward. Those that last year had fewer minutes have more this season."