Lovegrove, 26, has spent the past seven years at Hull KR, and can fill in at centre or in the pack.
McCormack said: “I only named 23 players last week because I wanted to keep one space free until the deadline today.
“I was concerned about our lack of options at centre. Rhys can play there or in the second row and we were only one injury away from a major problem at centre. He’s been in our thoughts for a few seasons now but for various reasons has never played. He needed to sort out a couple of issues to ensure he would be available for the month but will join us a week on Monday.”