The popular New Zealander back-row has played more than 100 games since joining from Melbourne Storm at the end of 2014.
Moors, such an explosive ball-carrier, helped Castleford win the 2017 League Leaders’ Shield when they finished top for the first time in their history and he also played in that year’s Grand Final loss to Leeds Rhinos.
At 34, he has not been offered a new deal but Powell said: “Junior has been a phenomenal servant to the club and been fantastic during his time at Castleford.
“He is a top-quality fella and towards the back end, when he got over the terrible injury he had, he has been pretty strong.”
Fellow forward Matt Cook has already confirmed his move to Widnes Vikings while Mike McMeeken is expected to join Catalans Dragons in 2021.
Powell expects to run with a smaller squad next year but is not unduly worried given how so many youngsters and fringe players have stepped up this time around.
Hooker/loose forward Jacques O’Neill has been praised for his impact while it was today announced Tyla Hepi has seen the option on his contract triggered to take in 2021.
“Even though the numbers in our squad will be a little bit less next year, I think the quality will actually be improved, depth-wise, because of what these young guys have done,” said Powell.
Castleford have already announced the capture of Salford Red Devils full-back Niall Evalds for 2021 while Gareth O’Brien - the full-back who has impressed while on loan from Toronto Wolfpack since July - is also set to see his move made permanent.