Below is what I am planning on doing with my forum, could someone tell me, will making the forum a sub domain like below affect it's search engine ranking or not?

I have the URL set as forums.wrestling-kings.com right now but I want forums.wrestling-kings.com as a subdomain so I can make my portal wrestling-kings.com

I got the domain made. Then, I want to make a subdomain called forums.wrestling-kings.com/index.php?]forums.wrestling-kings.com. I am using a CNAME record (required for urls on my host) on the forums.wrestling-kings.com and using an A record (used for specific sites) for the forums.wrestling-kings.com/index.php?act=site]portal.