Connor Galvin performed well for the most part in the pre-season opener at the Giants. He played LT in the 1st Half and was in at RT in the 2nd Half when he suffered the injury.
It's highly likely that Galvin will clear waivers. It's realistically possible that the Lions will work out an injury settlement with him.
If the injury doesn't involve the ACL, I think Galvin will be healthy enough to play late in the season. I can envision the Lions and Galvin coming to a Practice Squad contract agreement sometime in the 2nd half of the season.