Filtering by IP address won't necessarily work because, if the Laptop in question gets its IP address by DHCP, the address can change. If it is connecting "wirelessly", you'd be better blocking it with MAC address filtering.
Your router should show those computers which are connected to it together with the MAC address of their network adapters. Enable MAC address filtering and then enter the MAC address of those computers that you do want to allow to connect.
This does mean that the Laptop whose address you haven't added won't have access to either the Local Area Network or the Internet.