How do I make sure that freelancer cannot claim intellectual property rights for an asset?

This is the kind of thing a work-for-hire contract addresses specifically. It will/should include a term indicating that the freelancer assigns all intellectual property rights to the contracting entity. If you are working from a freelancing site, check out the terms of service. For instance, Fiverr includes the assignment by default in the terms of service. For confidence, you might confirm this with the freelancer so that you don't get in a conflict anyway.

Fiverr FAQ: "Ownership and limitations: Unless clearly stated otherwise in the Gig description text, when the work is delivered, the buyer is granted all intellectual property rights, including but not limited to, copyrights for the work delivered from the seller and the seller waives any and all moral rights therein. All transfer and assignment of intellectual property to buyer shall be subject to full payment for the Gig. For more information of ownership of materials, please see our Terms of Service “Ownership” section here."