Coly moves for the money
Senegal defender Coly has originally signed on a loan deal that will start in January and expire at the end of the season, although it is thought he will sign a three-year permanent contract should Steve Bruce's side avoid relegation.
Martel said he had offered Coly a new deal, but he refused in order to get more money from signing on at St Andrews, although he does not blame him for wanting to cross the English Channel.
"Ferdi wanted to leave. And when a player wants to leave for England, it is already settled," said Martel.
"He didn't find a top level club, but he will earn three times what he earned with us. Like usual, it is a money matter.
"But I have nothing against Ferdinand. In his position, perhaps I would have taken the same decision."
Meanwhile, it seems that Didier Domi could also join Birmingham soon, as the PSG full back has hardly played this season with Luis Fernandez at the helm.