Tensorflow installation missing dependency

Thanks in advance for any help.

Trying to install and run Keras and Tensorflow. Install_tensorflow() produces the error that

.virtualenvs/r-reticulate/bin/pip: is missing

and it is. I found the advice on the community from @andrie that;

library(tensorflow)
install_tensorflow()

should work but not in my case. I am running Pop!_os (an Ubuntu derivative ) and have Python 3.7 installed.

What have I overlooked?