The Norwegian performed at Old Trafford in the Red Heart United Legends game against Real Madrid at the start of the month and defended valiantly alongside Jaap Stam at the heart of the back four.
"I am doing some coaching," he told ManUtd.com. "A little bit of coaching work and I'm also doing the actual coaching badges. I took a bit of a break when I finished playing football, four years ago now, but I am getting back into it again."
Johnsen suffered from knee problems during his playing days which contributed to an extraordinary record that saw him winning a trophy in four consecutive games at the turn of the century. After being a key part of the Treble-winning team, he was sidelined for most of the 1999/2000 campaign before returning at Southampton - when the Reds clinched the retention of the Barclays Premier League title.
"I played in all the final games in 1999 and was then out for nine months or something," the 44-year-old recalled. "I kept playing in 1999 even though I needed an operation on both of my patella tendons. It took me a while to come back but I guess I returned just in time, which was quite funny!
"I have this tendons problem but it's actually okay now. 'Jumpers' knees' were not nice to have and it took me a while to get back from it but there are no problems now."