As this can be caused by a number of things (trauma, minor infections, irritation of the skin, etc), it's always a good idea to have a vet take a look in person when there is a sudden change on the skin, especially if the change is rapid, painful, or bothersome to Banks.
In the meantime, it's a good idea to keep the area clean and dry, and continue to monitor it for any additional changes, or see if it resolves. If the spot continues to grow in size, is bothersome or painful, begins to ooze debris, becomes discolored, or doesn't resolve in a few days, a vet check is best to rule out more serious issues.