"He's (Mannering's) played a lot this year so we want to keep him fresh and ready to go. It's all part of the process.
"It was a pretty tough game at the weekend so some of our individuals need to be managed week to week."
Johnson brushed off concerns over his fitness and said he was conscious of not overdoing it four days out from his milestone match.
"I'm feeling good. It was a tough game coming off a bit of a break," said Johnson.
"The legs probably blew out a bit quicker than they usually do and I just pulled up a bit tight.
"Today was just making sure I was all good but I didn't want to push it."
Interchange front-rower Charlie Gubb is unlikely to play after a head knock forced him off during the second-half against the Storm. McFadden said the 25-year-old will be given the chance to prove his fitness, while 18th man Sam Rapira is ready and waiting to fill his place.
The Warriors are already resigned to being without Konrad Hurrell (shoulder) and Manu Vatuvei (shoulder) for the Roosters clash, although both players completed training this morning.
Back-rower Ryan Hoffman did some light running with training staff as he continues to recover from a calf injury suffered in last week's State of Origin decider.