BCCI have announced their retention policy ahead of IPL. Each team can retain 5 players. But a new rule came into the limelight which will benefit CSK. 

According to this rule, any India player who retired 5 years ago from international cricket will be now considered the uncapped player. 

This rule was introduced in the first season of IPL, but no team has ever used it, it was removed from the rule book in 2021 but again BCCI came with this rule. This will now benefit CSK as they can buy Mahendra Singh Dhoni in 4 cr only as he retires in 2019 from international cricket.