The shale natural gas upswing in the U.S. has been well documented, but closely watched short-seller Jim Chanos told CNBC he's a "glass half-empty kind of guy," and there's a downside to boom.

At historically low nat gas prices of around $3.75 per million British thermal units, "some of the levered players are struggling to cover their debt service and their obligations to drill more holes under their leases," Chanos said on "Squawk Box" on Thursday.