McClellin, who was previously placed on injured reserve with an undisclosed injury, is dealing with a concussion and recently suffered a setback in practice, Jeff Howe of the Boston Herald reports.
The linebacker was eligible to return from IR this week, but the setback now puts McClellin's season in jeopardy. It looks like the Patriots will remain as cautious as possible with McClellin given how long his recovery from the concussion has dragged on, so look for the team to instead use its two available slots to activate players from IR elsewhere.