Hi Roger,
I have seen this.
The leg may have been injured when the frog was younger; perhaps when being put into a transport container?
Or
It may be undeveloped ?

The frog will very likely do just fine; especially for this species that does not climb.
Observe him with his tank mate(s) to be sure he is not being bullied.

I believe the biggest concern is how it will do during / after a shed.
If you ever notice extra skin getting stuck you may have to transport him to a confined container w/ a little distilled water on the bottom of the container.
A little soak will help remove the extra skin.
This is stressful~~so do this only if absolutely necessary.

Just wondering , how long have you had this frog?