Karen Khachanov is working with former No.3 ranked tennis player, Nikolay Davydenko, on an unofficial basis. This collaboration is not officially sanctioned by any governing body, suggesting it may be a private arrangement between the two players.
The nature of their work together is not explicitly stated in the provided evidence, so it is unclear what specific aspects of their game or careers they are focusing on. However, the fact that they are working together implies that they are likely sharing knowledge and expertise to improve their respective skills.
It is worth noting that the evidence does not provide information on the duration of their collaboration or the specific goals they are working towards.