"With his age there are always going to be a question mark but if his work-load is handled right then his Test career is far from over," said Johnson. "Colin is a true professional but he just looks like a player who is tired. I've been up front and honest with him and told him that he needs a break.
"You need to take the right approach with the demands on modern players and it's only fair on him that he has a rest. He's had a big year for Wales and Newcastle. He's an experienced player who offer a lot to the squad and we want to make sure we keep him around this week."
Skipper Michael Owen retains his place but is shifted across to fill Charvis's place on the side of the scrum to make way for Scarlets No.8 Alix Popham. Popham starts his first RBS Six Nations game, three years after making his Wales debut, while Dafydd James and Mike Phillips replace injured pair Mark Jones and Dwayne Peel.
"It's been difficult because it's always hard when you're not being picked for the big games," said Popham. "I've kept quiet, put my head down and trained hard when I've been back with my club. I'm really looking forward to Saturday."
There had been calls for Johnson to make wholesale changes to the side held 18-18 by Italy and heavily beaten by England and Ireland. Johnson said: "We thought about a few positions but we have to consider what is appropriate for the team and the country. The problem we had is that some kids had not had enough preparation."
That means no place in the starting team for Gavin Henson who is handed a place on the bench for the third time since completing his seven-week suspension.