The outgoing governor of the Bank of England (BoE) has highlighted the potential risks to monetary governance if a central bank digital currency were to be launched in the U.K.

In a foreword to a BoE working paper on Thursday, Mark Carney wrote, “While CBDC (central bank digital currency) poses a number of opportunities, it could raise significant challenges for maintaining monetary and financial stability.”

As reported by Reuters, Carney added that a digital pound would have to be “very carefully designed” if the central bank went ahead with a launch.

The comments will be among Carney’s last as BoE governor. The Canadian will leave the central bank Friday for a new role as U.N. special envoy on climate action and climate finance. He will be succeeded at the BoE by Andrew Bailey, current head of the Financial Conduct Authority.

In past comments, Carney has appeared relatively pro-cryptocurrency for a central banker, saying bitcoin’s (BTC) rising value was no threat to financial stability. He’s also suggested a digital currency could one day replace the U.S. dollar as the global reserve currency.