Panthers quarterback Cam Newton did not participate in Wednesday’s practice, and his status for Sunday’s season opener is murkier than it has been.Newton, who cracked his ribs less than two weeks ago in a preseason game against the Patriots, appeared in good spirits during the portion of practice that was open to the media, but he did not throw a pass. Wearing a large flak jacket with extra padding, he stood behind the other quarterbacks and watched as they went through group drills with receivers.Last week, when asked about his chances of starting against the Bucs, Newton quickly replied “there’s not doubt in my mind.”But while head coach Ron Rivera claimed Newton hasn’t had a setback, it’s clear his quarterback is still experiencing a good deal of pain.When asked if Newton’s nonparticipation was a planned part of his recovery, or a product of soreness, Rivera answered, “A lot of it had to do with the way he felt.”Rivera later added, “I expect him to be there (against the Bucs), and we’ll see how it all unfolds.”Newton’s weekly media appearance before regular-season games is on Wednesdays, but he was not available because he was undergoing treatment. A member of the Panthers PR staff said the hope is Newton will be able to go on Thursday.Of course, there’s a chance the Panthers could be purposefully sending mixed messages down to the Bucs. But Newton starting on Sunday should no longer be considered guaranteed. Even his always-positive coach left the door open for the possibility of the Panthers beginning the season without their most-important player.”We’re going to approach this day-by-day, but I’m an optimist. I always look at things half full. I’ve been wrong before, but we’ll see,” Rivera said.