Arsenal travel to Stamford Bridge on Sunday for a crunch clash with their London rivals.
Wojciech Szczesny had a mixed time this week for Arsenal, enjoying a comfortable match against Galatasaray midweek only to be red carded for cutting down Burak Yilmaz.
Though he is now set to sit out the next few Champions League games, the Arsenal goalkeeper is more than looking forward to the second successive London derby back in the Premier League, with a visit to Chelsea on the horizon.
And despite the rivalry between the two teams, Szczesny has joined the growing list of admirers for Chelsea's newest battering ram of a centre forward, who has scored 8 goals in 6 games in England's top flight.
"[Diego] Costa is incredible," the Pole told the Arsenal website. "His partnership with Cesc Fabregas and Eden Hazard has been incredible and, at the moment, he's looking as dangerous as any striker in the world.
"We've got huge respect for him and we know how dangerous he is. I think he's scored in most games so it'll be a tough test."
The Gunners have traditionally had problems with another powerful forward in the Blues' history, Didier Drogba, but despite the Ivorian's return to Stamford Bridge, it is the club's former Atletico Madrid striker that has helped turn the Blues into one of the best attacking sides around, according to Szczesny.
"At the moment [Chelsea] are as good as you will get in Europe," he said. "They score goals and they’ve always defended very well so it’ll be a very tough test but it’s one that we’re looking forward to.
"Hopefully we can leave last season’s result behind us and show that we can get the result against them."