The Treble winner was a key part of the unparalleled success in 1999 and has only fond memories of working with the duo, who have both called time on their careers over the past few days.
"Paul has been an absolutely fantastic player for the club for all those years," Johnsen told ManUtd.com on Thursday. "When you win something when you retire as well, it's always a good way to go.
"What can I say about David Beckham? I've been lucky to play with him as well. He has always been such a professional to the game. There were always so many things happening around him but he always managed to be 100 percent on the pitch.
"So that was something that impressed me every time actually and to go on and be so professional until 38 and still have the lifestyle that he has is unbelievably impressive actually.
"You can go and play football as long as your heart is there and he has had his heart there for so many years. All these things were happening around him but his heart was in playing football - that's what he loved and still loves.
"That's the way he is. He is such a nice guy and I think he showed that to so many people around the world and that's why he is so popular."