I encountered this case when using the Ubuntu 18.04 OS. It turns out that the pip program is not installed on my system. Make sure pip is installed on your system. If not, then do the following steps to install it.
Update you repo
sudo apt update
Then, for Python 2.x
sudo apt install pip
Or, for Python 3.x
sudo apt install pip3
Now, try to create new virtual enviroment.