Hi
No, you will not.
Historic Health and Activity data - including from workouts - is stored on your paired iPhone, not on your Apple Watch.
Follow the instructions here to unpair your old Apple Watch (which will include syncing your current day's Activity data to your iPhone) and then pair your new Apple Watch. The current day's Activity progress will be retained regardless of the time of day at which you carry out the process:
Be sure to unpair via the Watch app whilst your devices are connected via Bluetooth. In addition to erasing the old Apple Watch, this will remove Activation Lock, leaving your old watch ready for a new user to set up as their own:
About Activation Lock on your Apple Watch - Apple Support
If preferred, you can keep both watches paired to your iPhone, switching between them as and when you wish. Activity data will also sync between them as you do so (only one Apple Watch can be active at any given time):
Use more than one Apple Watch with your iPhone - Apple Support