Yes. In order to complete the registration process and activate your sample license, you will need an ISRC for your derivative song. if you don't currently have an ISRC, then below is advice on how to proceed.
If you don't intend to release your song/track in a way that will create an ISRC
Currently it isn't possible to obtain a sample license without an ISRC. If you aren't using a label or distributor to release your music, you will need to get your own ISRC from the issuer in your territory. You can find a list of ISRC agencies here.
If you will get an ISRC when I upload my song with my distributor.
You can complete all the other steps in the registration process, including the payment stage, and then proceed with the upload with your distributor. You can obtain a draft license if your distributor requires one and then, once you have an ISRC, you can complete the registration and activate your license.
If you plan on having a label release your track for you.
The person or entity that is responsible for releasing and accounting for the song should be the one holding the license. The licensee will need to report the full revenue of the song and this might be easier for your label to do themselves. You can find out how to send the song to your label here.