The manager believes that his new signing has already given fans a taste of what is to come after scoring in his competitive debut in the DFB-Pokal first round
The Finnish coach saw his side easily overcome their hosts in the first round of the DFB-Pokal on Saturday in their first fixture of the new season.
Speaking after the game, the former Liverpool defender was quick to stress that the club's new acqusition had shown he could flourish after arriving from Hamburg this summer for a reported fee of €10 million.
"[Son] came into training later than the others," the 39-year-old Finn was quoted by Bild am Sonntag.
"Sonny has shown that he is a good player. And the team will now be even stronger."
The 21-year-old South Korean forward scored 20 times in 78 games for Hamburg and also has 17 senior caps to his name, grabbing two goals for his country.
Bayer Leverkusen face Freiburg on August 10 in their opening Bundesliga game of the new season.