Nothing is gained by delay. The employee's problem will get worse: any co-worker tensions will increase. The negative impact on your workgroup will continue.
Schedule the 15 or 20 minutes that the interview will take with the employee. Be sure the setting is private and that you will not be interrupted. Make this appointment a matter of immediate importance. Don't put off the session or allow the employee to do so. The employee must clearly understand from the outset that you want to speak to him or her immediately.