Following a tough challenge from Julio Arca, the striker bit the dust and looked in real discomfort when leaving the field.
There are just three games remaining before Shearer hangs up his illustrious boots, plus of course his testimonial, and the veteran feels he may be forced in retirement.
Shearer: "It does not look good. I think someone fell on me and I twisted awkwardly. I may have a tear in the medial ligament and that would be it for me if it is the case.
"It is sore at the moment and does not look good. I am keeping my fingers crossed, but it is certainly sore at the moment.
"It's a great way to go out if it is. I've been waiting five or six years for a penalty against this lot because I missed my last one against Sunderland, and the wait was worthwhile. There was a lot of frustration and anger in that penalty.
"It was a tremendous turnaround from us because we were rubbish in the first half and the manager has come in and let us know what he expected from us. To be fair to the boys they've delivered that in style."