I am a manager for a small company, with different teams working under me. One of the managers I manage is very career focussed and cut throat, which is good in some ways but he is not a team player and aggressively fights to overachieve. This creates a backlog of work for other team members to achieve and is unrealistic, damages quality of service and has rapidly effected the dynamics of the wider team. He refuses to take any advice from me and any time I provide guidance on the core business and effects of his approach, is taken above me and reported as disrespect to him and his position. Every decision I make is challenged or ignored, which makes it impossible for me to manage the wider team as I am constantly undermined.
If the quality of service continues to drop as we drown the other staff in work they cannot physically complete, the business will decline and potentially cease to exist. I do not know how to manage this man because he has a lot of potential and could go far but I cannot allow this approach to damage the business and potentially lose other team members due to undue stress.
My manager is very supportive of me and my decisions but I am struggling with how to approach the situation. In a perfect world I would keep all staff members and refocus the work on the reputation we want to maintain but I don't think that this is a possibility at this stage. This is spilling over into my personal life, I can't sleep, lose concentration and feel overly stressed all the time to the point I am questioning staying in the role.
Any advice on how to effectively manage this situation would be greatly appreciated.