The England hooker, 31, came off in the early stages of Thursday's win at Hull FC with an abdominal injury.
McShane, 31, was clearly in some pain and, unsurprisingly, has not been included in tomorrow's squad for the visit of Wigan Warriors.
However, Powell said: "We don't think it's as bad as we first thought.
"But we’ll see how it settles in the next couple of days and then he potentially has a scan next week.
"Obviously he’ll be missing tomorrow but I thought Adam Milner slotted in really well last week so he’ll get that job again."
England loose forward Milner spent the first part of his career at No9 and obviously knows the role well.
If, though, Castleford are to maintain their current form - they have won their last four games to surge into the top-six and keep alive play-off hopes - they will be wanting reigning Steve Prescott Man of Steel McShane back as soon as possible.
Asked what his gut feeling is, Powell added: "It’d be hard for me to say time-wise but the gut feeling is he’s a quick healer.
"He rarely gets injured and gets through things pretty quick so that’s what we’re hoping for.
"He’s obviously a pretty important member of our team and we want him back for this really crucial period of the season.
"His gut instinct is he thinks he’ll be okay but we’ll wait and see on the scan or how he settles before Tuesday."
Powell continued: "It’s an oblique injury.
"I don’t really know much more and the physios don’t really know the detail as it’s quite deep the pain that he’s getting.
"But he has settled down pretty well and I’m hoping he’ll be okay."