You might think your top performers are with your team for the long haul. But according to a recent study, they're actually the most likely to face burnout.

The study--conducted by researchers from Yale University, the University of Leipzig, and the WHU-Otto Beisheim School of Management--found that about 20 percent of highly-engaged employees reported feeling burnout. Researchers terms them the "engaged-exhausted" group of employees. Those who face burnout tend to be both physically and mentally drained, and are less likely to be productive--harming both employees and your business as a whole.

Do you recognize the signs of employee burnout? If you think a top performer--or any other employee--is at risk for burnout, use these three strategies to keep employees productive and happy:

1. Continuously hire.

Some employees feel the effects of burnout because they're doing the work of more than one team member.

Whether your company is rapidly growing or an employee leaves your team, an open role means other employees need to pick up the workload while you look to hire someone new. To ensure your current employees don't get overworked when you have a seat to fill, follow a proactive recruiting strategy to build a pipeline of candidates and speed up your hiring process.

Always have at least a few open roles posted on your career site. This is especially important for high turnover roles and roles you need to fill several times throughout the year.

With a continuous recruitment strategy, you can hire new employees in anticipation of the need, rather than scrambling to hire top talent when you have an immediate opening. This will speed up your time to hire and ensure your top employees don't get overworked taking on the responsibilities of an open role.

2. Regularly touch base with top performers.

Your top performers might be too busy to reach out and ask for help--until it's too late. While underperforming employees might need the most attention and coaching, it's arguably more important to check in with top performers on a regular basis.

Ask how their workloads are and if there's anything the company can do to to make their lives easier. If resources--such as project management software or professional development tools--are available to help your employees be more productive while avoiding burnout, invest in these resources if you have the budget to do so.

Also ask top employees which projects they're passionate about and which tasks aren't their favorite. While you can't promise employees they'll no longer have to do certain tasks, you can help them complete more projects that get them excited to come into work every day--ultimately keeping employees motivated and less likely to burn out.

3. Hire and promote more managers.

Top-performing employees are often promoted to management roles, meaning they have a great opportunity to manage and mentor fellow employees. That also means they might have less time to dedicate to their day-to-day work as individual contributors.

Keep an eye on how many direct reports each manager has and as your company grows, hire new managers--or promote from within--to ensure no employees suffer from managing too many people. The right number of direct reports varies depending on your company's organizational structure and each manager's responsibilities.

According to the American Management Association, a manager's number of direct reports shouldn't exceed the number of days in a work week: five. This ensures managers have plenty of time to meet one-on-one with each direct report one day a week and still have time to complete their day-to-day work.

Burnout poses major risks to any company's productivity and profitability--and the health and wellbeing of employees. By following these tips and taking other proactive steps to prevent burnout, you can improve employee satisfaction and overall business productivity as a result.