I'm not following why the Lions would want or need to cut him, versus just placing him on the reserve/retired list. Either option gets them the cap room they need, if this is true:
If he announces his retirement, the Lions place him on the reserve/retired list, and gain the cap room right away.
If I understand correctly, they'd only need to cut him if he came back and said, no, I'm not retired after all. Then they'd have to reinstate him or cut him. And they wouldn't have the cap space to reinstate, so they'd cut him at that point.
As I said, it's timing. As in: The timing of when Calvin Johnson
formally retires.
Calvin has told the Lions he is going to retire, OK, fine. That doesn't do them any good, in terms of cap space. They are holding 24 mill on the cap for him, right now.
They cannot place him on the reserve/retired list until he files the paperwork/announces his retirement, etc.
If Calvin takes his time with the decision, or doesn't bother to file the paperwork, it puts the Lions in a bind, in terms of cap space. Gaining 11 mill in cap space in March is a LOT more helpful than June. Lions have 18 mill to spend, if you leave 7-8 mill for rookies, and a little wiggle room to start the year, Calvin's salary would double their cap space for 2016.
Calvin can ensure that the Lions don't go after his pro-rated signing bonus, by dragging it out, and perhaps forcing the Lions to cut him, so they have access to that cap space. Then, he can retire, and not owe any money. It would be a bad business decision to retire anytime before free agency started.
We shall see what Calvin does. I have no reason to doubt his sincerity, but there are business reasons why he could just be threatening to do this.
I'm real happy everyone thinks Calvin is a swell guy and all, but business is business.