Kevin-Prince Boateng's proposed transfer from Schalke 04 to Sporting Lisbon has collapsed in curious and confusing circumstances.

On Wednesday, BILD quoted the player's agent as saying that “we have failed to reach an agreement over image rights”, contradicting earlier reports in the Portuguese press that Boateng, 28, had failed a medical upon arrival in Lisbon.

Schalke players struggling to earn moves away

This would have been the third time this summer that the transfer of a Schalke player (after Felipe Santana to 1. FC Köln and Sidney Sam to Eintracht Frankfurt) had collapsed at the hands of the purchasing clubs' medical teams.

Boateng's agent quickly dismissed those reports as “ridiculous”, whilst the German club's official Twitter account assured fans that “Negotiations are continuing as normal”. Several hours of international confusion ensued. 

It was finally cleared up on Thursday morning when the Lisbon club confirmed that the deal did indeed collapse due to a failure to reach an agreement of over image rights. Sporting Lisbon are said to have wanted a majority stake in Boateng's image and advertising rights. The player on the other wanted to retain full control.

A transfer that failed to live up to expectations

Boateng's contract at Schalke runs until 2016, however he has been suspended by the club since May. Since joining the 'Royal Blues' for 12.5m euros in 2013 to much fanfare, the Schalke hierarchy have since been less than impressed with his performances, attitude and body language on the pitch. 

The final straw came towards the end of last season in May 2015, when, in the wake of a humiliating 2-0 home defeat to newly promoted Köln, the club from industrial Gelsenkirchen announced that Boateng - along with Sidney Sam - had been suspended and were free to leave. 

The club stated at the time that the players were not worthy of the shirt, and that the "trust relationship" had broken down.