John Mack on Morgan Stanley, China and Brexit

Former Morgan Stanley CEO John Mack shared his thoughts on where he sees the biggest risks in the world today, the likelihood of a Brexit and his outlook on China.

"I think the biggest risk is geopolitical risk," Mack said in the CNBC interview, explaining that like boiling water, rising tension from world events could easily spill over and cause a large mess.

The former chief executive also discussed his views on shares of Morgan Stanley, which are in bear market territory, down more than 36 percent from a 52-week high reached in July, as part of a larger decline in bank stocks which are getting squeezed by falling rates.

To watch the full broadcast interview with the cast of CNBC's "Squawk Box," you must be a CNBC PRO subscriber.