Nathan Thompson cleared Drew Talbot of any blame after being left unconscious.
Thompson believes the fault lied with him after the aerial collision with his Pompey team-mate against Oldham.
The 26-year-old was taken to hospital after being left out cold, but explained he feels he was in the wrong.
Thompson said: ‘It was a freak incident. Nothing like that has ever happened to me before.
‘I didn’t know where Drew was. I should have commanded the situation and made a louder call.
‘In fairness to him, I was in his position and he was heading it. It was totally my fault.
‘I watched it back and I felt sorry for him. It’s not nice to see your team-mate down in that way.
‘Drew messaged me that evening and told me he was thinking about me and had hurt his jaw. I completely take responsibility for what happened, though.
‘Each concussion is different and affects people in different ways, but it’s positive that I recovered okay and feel fine now.’