The new CSL rule:
After the CSL clubs went on a spending spree in the previous transfer window and at the start of the current one, the league authorities took it on themselves to reduce the amount of money spent and came up with a smart plan. They have introduced a new rule that allows just 3 foreign players to play in a club, giving all the clubs a big shock. This rule will make sure that players who are offered regular football will only make the move. Costa, as good as he is, might not be able to play every game and it might surely have an effect on his performances.
The quality:
And finally, the biggest difference between the leagues in Europe and in China is the quality of personnel in the teams. The CSL clubs have a couple of players each of top quality but they are filled with players who are still learning the game. Costa is in the prime of his game and could be a world beater if he can continue his good form. He may break a number of records in China, but winning the Champions League, the Premier League and such competitions is something that will be out of his grasp. Surely, he should snub the clubs from China at least to keep up his quality.