Powell said: “It looks bad. He’s got fractures in his face and his cheekbone. His jaw and his teeth are numb.
“We’ll have to wait and see how he recovers to see whether he can play again this season, hopefully he can.”
Six weeks will take Castleford to the end of the regular season and they are currently outside the top six.
The Tigers are still three fixtures short of reaching the minimum of 18 to qualify for the play-offs and Powell reckons they need to win six of their remaining eight games to keep alive their hopes of extending the season.
Powell added: “Shenny’s been a champion player for this club and I think we all owe him the opportunity to play again.
“To do that, we’ve got to go past six weeks. It’s a decent challenge but we’ve got to attack it with real positivity and see where it takes us.
“I think Michael Shenton has to be one of the reasons we go after this and give everything that we’ve got to make it happen.”
Castleford have lost seven of their last eight league matches but will have the bulk of their Challenge Cup final team back for Friday’s game as they look to make amends for their 60-6 rout by the Rhinos on home soil in May.
Powell said: “We’re not worried about anything that’s happened this year, it’s about what happens now.
“We had 15 players with Covid last week so the team is going to look very different this week.”
Prop Liam Watts remains absent with Covid-19 protocols while stand-off Jake Trueman continues to be plagued by back trouble that Powell says may require surgery.
Powell continued: “It’s taken a long time to come to an understanding of exactly what’s happening with his back. I think we’re coming to the point where it will get resolved.”
Leeds are without scrum-half Luke Gale through suspension while prop Mikolaj Oledzki is injured, but Powell said: “They’ve got good depth and I would say they’ve probably the best young players in the comp right now.”