Links in mattermost domain don't open from chat

Hi all... I have mattermost running behind a reverse proxy, at the root.. So, say

[edited... I can only include 2 links in this post since I'm a new user, evidently... ]

foo.example.com/

I have the proxy server redirect /stats/ to another server.

So,
foo.example.com/ => mattermost
foo.example.com/stats/ => some other server

That works all fine and well. But when I link to https://foo.example.com/stats/ in a mattermost chat, users are redirected to the choose a team page instead of actually loading this address.

Is there any way to stop mattermost from hijacking these URLs?

Thanks!