The club made an official statement yesterday afternoon.
Charlton plc chairman Richard Murray said: "Eleven days ago Smertin (Russia’s captain) advised Alan Curbishley that he no longer wished to play for our club due to a lucrative three-year contract offer from Dynamo Moscow."
"We were in discussion with Chelsea officials all over the weekend regarding Smertin's complex contractual situation. Smertin had one year left with Chelsea and his season-long loan agreement contained an option, which we could exercise at the end of the current season to sign the player from Chelsea for £1m. Both clubs have reluctantly agreed to release the player from his obligations with immediate effect. No words can adequately express how angry and disappointed we are that he felt unable to honour his obligations to us."
"We have done everything possible to persuade the player to stay but there is little point in keeping a player when he is so determined to leave. We also have to take account of the effect on all the other players at the club."
Source: Official site