Borussia Dortmund are prepared to sell teenage striker Youssoufa Moukoko having recruited Serhou Guirassy from VfB Stuttgart, Sky Sport TV reported on Saturday. The Black and Yellows landed in Thailand for their pre-season tour with four main strikers on their books and at least one seemingly set to leave. Sky said 19-year-old Moukoko was being made available for around €20 million ($22 million). Media reports had previously considered Ivory Coast forward Sébastien Haller to be the first candidate for a sale. The future of Germany striker Niclas Füllkrug is also unclear. Sky said Füllkrug want…