Here's the biggest challenge facing business leaders, according to ex-Yum Brands CEO

• David Novak says 7 in 10 employees in the U.S. are not engaged.
• "They're going to work and they can't wait to go home," he says.
• Novak says great companies create environments where everyone counts and is valued.

Former Yum Brands CEO David Novak told CNBC on Thursday the biggest challenge facing business leaders is getting employees engaged.

"Seven out of 10 employees today are not engaged ... and 20 percent are disengaged. You've got on average 30 percent of your employee base driving your results," Novak said on "Squawk Box," citing a recent Gallup survey.

"They're going to work and they can't wait to go home," he said. "Versus, you know, tap dancing to work."

According to Gallup, engaged employees "are involved in, enthusiastic about and committed to their work and workplace." Gallup's results are based on telephone interviews with about 1,500 working U.S. adults.

Novak, who spent nearly 20 years at the helm of Yum and doubled the size of the company to 41,000 restaurants, according to his LinkedIn, said great companies create environments where everyone counts and is valued.

"They have to create that culture where everyone feels like they can make a difference, he said.