That was the warning from the European Data Protection Board on Thursday (February 20).

It's the latest to add a critical voice to the deal.

Google announced the deal in November last year.

It wants to compete with Apple and Samsung in the crowded market of fitness trackers and smart watches.

Fitbit trackers and other devices monitor daily steps, calories burned and distance travelled.

They also hold the key to a trove of health data gathered from the devices.

Giving U.S. tech giant Google such access is worrying, the EU privacy watchdog said.

It urged the companies to mitigate possible privacy and data protection risks before seeking EU antitrust approval for the deal.