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He’s out of a cast, but when will Dolphins quarterback Ryan Tannehill be back on the field?

Per a source with knowledge of the situation, the week-to-week scenario has now become day-to-day for Tannehill, who suffered 15 days ago a Grade II MCL sprain and a slight tear of his ACL on a low hit from Cardinals defensive lineman Calais Campbell. With the cast, which was used to stabilize the knee so that the MCL could heal, now gone the question becomes whether the MCL has healed enough to let Tannehill play.

There’s also a question regarding whether the Dolphins are comfortable letting Tannehill play at all with a slightly torn ACL. As NBC Sports Medicine Analyst Mike Ryan explained in the aftermath of the injury on PFT Live, the ACL doesn’t heal itself. So the damage will never get better on its own — and it could always get worse.

The Dolphins haven’t been any worse with Matt Moore playing for Tannehill; Moore led the Dolphins to a win in the Arizona game and victories at the Jets and at Buffalo. Still, Tannehill is their primary option, and they’re holding out hope for getting him back for the postseason.

One key wrinkle is coming; when the non-playoff teams have their seasons end and the process commences for signing players to so-called “futures” contracts, the practice squads of the postseason franchises become vulnerable to pilfering. If Tannehill isn’t going to play again this year, putting him on injured reserve would allow the Dolphins to call up a member of the practice squad, who then would be unavailable to be signed away.

And so the real question is whether he’ll be placed on IR before Sunday, when the season ends for 20 teams. If not, it will be time to wonder whether Tannehill will be back from his Grade II MCL tear, which typically has a four-to-six week timeline, four weeks after it happened.