The England international has revealed he's been studying maths for several years.
"I like challenging myself, finding that will from within to do something different and become better," Johnson told the official Liverpool FC magazine.
"I've always liked maths. So I thought: 'Why not?' I'm not setting any major targets, putting myself under loads of pressure to complete everything within a certain time.
"An Open University degree is quite flexible. I'm coming up to the end of the second unit of three. There are different paths you can take with various options to reach the same end. As long as I keep enjoying it, I'll keep doing it."