The 35-year-old was once tipped to be a leading player for England. However, a motorbike accident back in 2002 left him in a coma for six days before his professional career eventually petered out.
Prior to his crash in Rome, the ex England youth international had been the subject of interest from Sir Alex Ferguson on numerous occasions.
"I'd just broken into the first team at Carlisle, wanted to continue playing regular football and I thought that I might have had to bide my time at Manchester United," he told BBC Sport. "They came in for me again and I went to Blackburn instead but that was due to Palace needing all the funds up front.
"United also triggered a clause in my contract and wanted to speak to me about a possible move just before I got on the motorbike in Rome. There is quite a lot to dwell on which is why it took me so long to get over it."
Jansen is currently a coach with non-league side Chorley.