“Still in the concussion protocol” likely means that he’s not cleared yet. I think they need to make sure there aren’t any setbacks with all of the steps, but I’m not positive.
So he's probably in Stage 4 (out of 5):
Here’s The 5-Step Concussion Protocol Gronk Is Going Through This Week
4. "Football specific activities." The player can participate in non-contact drills, including throwing, catching and running. On this step, the NFL protocol says there can be no contact with other players or objects, including tackling dummies or sleds. If the player tolerates this level of activity without any recurrence of signs or symptoms, he moves to the fifth and final step.
5. Full football activity and clearance. The final step of the NFL's concussion protocol allows a player to resume practicing without any limitations. After the team physician clears the player to compete, an independent neurological consultant (INC) must examine the player. According to the protocol, the INC "must be provided a copy of all relevant reports and tests, including the player-patient’s neurocognitive tests and interpretations.” If the consultant concurs with the team physician, then the player can participate in the next game.
Rationale for stage 4: Gronk was reportedly wearing a Red no-contact jersey. That is not "practice without limitations" as stated in step 5.
However, according to Reiss' tweet from last night, Gronk had hoped to be out of the protocol today (Wednesday) - with an indication that it's the doctor's call. That sounds to me like
Stage 5 - i.e., he practiced today and is now waiting for the INC to examine him in order to declare that he is no longer showing symptoms and can therefore come out of the protocol and play in the game.
If the latter is true, he could be getting cleared by the INC as we speak?