Tennessee fan? WarEagle probably won't help you (just kidding).
You are in the preseason stage the only thing you can do is ..
Promote someone on your staff (if they haven't signed a new contract this season) or coach search using "Unemployed" under team.
Three things you have to remember.
1. The contract has to be more than the highest paid coordinator.
2. As long as your contract meets the above criteria and is equal or less than your current head coach, disregard a pop-up window that says you have no money.
3. I cannot stress this enough .. coaches salary have NOTHING to do with the teams salary cap/dead cap.