Hamburg general manager Frank Arnesen has hit out at the behaviour of Wolfsburg coach Felix Magath after Ja-Cheol Koo's proposed move to the Imtech Arena fell through.
South Korea international Koo had appeared on the brink of a switch to Hamburg last month only for the deal to collapse in the final few days of the transfer window.
Danish boss Arnesen has expressed his anger at Magath, claiming the Wolfsburg boss changed his mind over the midfielder at the last minute.
He told Cologne-based newspaper Express: "These are manners I am absolutely not used to.
"Maybe I am not perfect in the German language, but my ears are very good and I simply know what we agreed to do.
"This is not the way you treat colleagues. Everything was sorted out before.
"On Sunday the player's agent and the player were supposed to come to Hamburg but then Magath said 'no, he's staying with us'."
Meanwhile, Hamburg have signed goalkeeper Sven Neuhaus on a one-year deal to ensure competition for regular shot-stopper Jaroslav Drobny.
Neuhaus, who was without a club after leaving fourth-tier side Red Bull Leipzig, spent time on trial at Hamburg before being offered a deal.
Coach Michael Oenning said: "To be prepared for every possibility inside our goal this season we have moved for Sven Neuhaus.
"Neuhaus had been with Redbull Leipzig. He was on trial with us and in this trial spell he impressed due to his motivation and skills."