Clark has signed for Wigan Warriors for 2020, but will not be joining up with them yet as he is believed to be heading for Leigh Centurions.
The Championship side are looking to bring Clark in for the rest of the season on a short term deal.
On Clark’s departure from Castleford, director of rugby Jon Wells said: “Mitch has left the Tigers to pursue another short-term playing opportunity.
“Mitch has recently found first team football hard to come by at the Tigers and all parties felt a move away would enable him to do what rugby league players like doing best.
“He’s been a great bloke and a big contributor at the club over the last 18 months and we would like to wish him all the very best for the rest of this year and as a Wigan player from next season.”