It'll happen for a few reasons. Check his morale. If it's really low (
) then I'd trade the guy since you're not gonna be able to sign him.
If you tried negotiating with him before, and gave him a low-ball offer, you will get the "Sorry, but I will not negotiate any further with you" message. There is however a likelihood of the player re-opening negotiations with you once the season ends, possibly even before then. Again, that's assuming his morale isn't low.