O'Brien has been on the sidelines for 16 months with a knee injury and said: "I never thought at any stage my career was over, but I did wonder when I would return, and I spent a lot of nights at home thinking about that.
"But there are some great people at Bolton. It was they who kept me going day in and day out through the bad times because there were many days when I didn't want to be there.
"The lowest moments were not knowing what was wrong and whether it was going to be sorted because I was told to rest and that didn't help. Then I had one operation and that didn't help either.
"Then I went to see the main man, Dr Steadman, and he diagnosed the problem straightaway. When he opened up my knee he could see exactly what was wrong, and he sorted it out there and then.
"I spoke to him the next day and he felt confident he had sorted out the problem and that I would be back in six months. When he said that I had more hope. It took the pressure off and put my mind at ease."