Toro Self Propelled front wheel dragging

Greetings,

I have a Toro 20005 self propelled lawnmower. The right front wheel drags from time to time, making it hard to push. It will turn freely if pulled backwards. When self propelled it works fine.

I am wondering if it could be in the gear box, but since the drive works, I am not sure.

What say the experts?

Thanks.

Ted