No, but Time Machine only uses one folder on an external HDD and has no problem with other existing, created by the user, folders.
But if your external HDD is not in the right format (file system), you have to re-format the HDD to Mac OS XExtended (HFS+) to use it as a Time Machine, but that will make you lose all your data on it. You could copy it to the MBP's HDD and then format and partition and then copy back.