I would ask for clarification, such as examples of some of the statements so that I make sure that I am understanding what the comments are, and then express my gratitude that the information was brought to my attention. Then I would take some time and think about who that person is and if you really the reason why they are making derogatory comments about me$.$ Is it what they are saying or how they are saying it$?$ It could be that they are truly unhappy and negative or just a miscommunication. I could just check in with the team and ask them if everything is going ok and if there is any issues that they would like to address.

No not at that time, I would want to investigate and get some more evidence that the employee is for sure stating derogatory comments about me$.$

Human resources can help with looking into the presenting issue and uncover the underlying issue. Sometimes managers avoid dealing with these types of issues because they can be difficult to resolve.