Sporting president Jose Bettencourt has described Joao Moutinho's behaviour as "deplorable" after the captain joined rivals Porto.
Moutinho, who had been at Sporting since the age of 13, has joined Porto for a fee of €11 million in a deal that will see defender Nuno Andre Coelho move to Estadio Jose Alvalade.
Bettencourt claims Sporting were left with little choice but to sell the influential midfielder due to Moutinho's conduct in recent weeks.
"Joao Moutinho's behaviour lately has been deplorable,'' Bettencourt said. "If I had not experienced the situation, I would not believe it was possible to descend so low.
"At the start of a new period, we had an orchard with a rotten apple, which would contaminate the group. And we could not continue with a rotten apple.
"The only offer we received was that of FC Porto. We tried to get him to wait longer, so that there might be some offers from abroad, but Joao lost his temper and forced an exit to FC Porto, telling us that he had given his word to FC Porto."