The Samoan second-row, 32, was only playing his second game back after two months out with a knee issue when he suffered the latest injury in last Friday’s 26-16 loss at Salford Red Devils.
He has since been informed he will need surgery and is unlikely to play again in 2019.
“It is a bad injury – he will need an operation on it – and you rarely see a fractured hip in rugby league,” said Powell.
“It was a really awkward tackle which put him in a very difficult position and obviously it’s a big and bad injury.
“Potentially he will miss the full season.
“It’s so unlucky for Junior. I’m disappointed for him and I’m disappointed for us as he’s an important player for us.
“For me, it was a bad tackle, swinging around someone’s legs like that.
“It’s not been referred which is disappointing.
“It’s a big one for Junior as he’d just come back from injury, played against Catalans, gets injured there and just got back again and got a big injury.
“He’ll be gutted.
“He’ll be having the op soon. I think there’ll be some pins involved in all that and they’re not great to be involved with.”
Castleford have lost three of their last four games to slip out of the top five and need a victory when they host improving London Broncos on Sunday.
Although former Melbourne Storm star Moors is out, they could welcome back scrum-half Jamie Ellis for the first time this campaign
The former Huddersfield Giants and Hull KR player, 29, suffered a serious knee injury prior to the pre-season friendly with Featherstone Rovers in January.
Powell said: “Jamie Ellis hasn’t played for a while but he’ll play this week if he’s okay.
“He’s just got a little bit of a niggle but he’ll play this week if he’s right.
“We know London will be tough but we have to concentrate on ourselves.”