"I think it will be fairly similar to last week. It was a bit of a baptism of fire for Tui but he did a really good job so that certainly gives me confidence to potentially give him some more time. We've got some experience there in Thomas [Leuluai] and he'll probably start the game."
McFadden said the full extent of Johnson's injury had yet to be determined.
"This one seems to be potentially a little tear. We thought he was travelling pretty well but obviously it wasn't as good as what we thought," he explained. "We weren't even expecting him at training today. We were happy for him to do some build-up work on the side. He felt pretty good in that so he wanted to go and have a crack but obviously that didn't last very long."
Leuluai, who has just returned from a three-month layoff with his own long-term groin injury (osteitis pubis), was not surprised Johnson pulled up sore.
"I can't say I'm surprised because sometimes you sort of feel all right. It's sort of like a trial and error type thing. He'll definitely learn from this. It's like a hamstring, you feel good, you get through training and then in the first minute of the game it goes. It's just one of those things," he explained.
"I definitely told him to be careful. He does a lot of kicking and he does a lot of running so he really has to be careful of the groin."
With just six rounds remaining, a third consecutive defeat would be a severe blow.
The Warriors face the prospect of having to do without Johnson, who before last Sunday had not missed a match since late 2012.
Fan's wit adds to atmosphere at Warriors games
Diehard Warriors fan Robert Harris is fast earning a reputation for producing witty slogans which he proudly brandishes from the eastern stand during games at Mt Smart Stadium.
Harris, a 10-year Warriors member, is a popular figure among supporters in bay 26, where his signs help add to the atmosphere and humour.
Before last Sunday's match against Manly, the 24-year-old warehouse supervisor attracted the attention of Sea Eagles back-rower Anthony Watmough, with a placard that read: "Hey Watmough we don't like Manly either".
The New South Wales State of Origin star stopped to read the sign and acknowledged Harris with a sly nod and a chuckle before pointing it out to halfback Daly Cherry-Evans, who also appreciated the gag.
Pictures of Harris' signs have been popular on social media and his antics have also attracted approval from the likes of The Footy Show co-host Erin Molan and presenters on The Matty Johns Show.
Harris says the attention they attract helps enhance the game day experience for himself and girlfriend Korina Teleso, and his special needs step-brother John Hoff.
"It's my treat to him, I take him to every game with me," Harris explains. "He was born with a hole in his heart back in Rarotonga, so there wasn't much help for him there. He's never really been fully functional. He's there with it and understands who the Warriors are playing.
"It's sort of the main kick he gets out of life, going to the Warriors games, or watching it on TV."
Earlier this season, Harris targeted two Penrith players, with one sign reading, "Our Johnson will make your Mansour" and another saying, "Run at Cat in the Hat Soward".
