The Dortmund supremo is hopeful that the Germany international will decide against a transfer following the arrival of the attacking midfielder.
The Japan international returned to BVB last week after a difficult two-year spell at Manchester United, whereas Reus is being heavily linked with a move away from Dortmund at the end of the 2014-15 campaign.
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Nevertheless, Watzke believes the signing of Kagawa is more proof that the Bundesliga outfit is on the right path and hopes Reus will realize that Signal Iduna Park is the place for him.
"Marco also sees what's happening here at Dortmund. I don't have any doubts about that," Watzke was quoted as saying by Sport Bild. "Marco and Shinji are very well capable of playing together. We have a number of great players in midfield now. It's the perfect mix of experience, dynamic players and players who can retain possession.
"The stiff competition for places that everybody's been talking about is something I have yet to experience in real life. We have to get to the point where we are able to replace one or two great players each game."
Reus has a contract with Dortmund until June 2017, but allegedly has a buyout clause that allows him to leave for 35 million euros in the summer of 2015.