The Manchester United centre-back played alongside O'Shea 18 times before the ex-Republic of Ireland international moved to Sunderland in 2011, with the last occasion being the Champions League semi-final second-leg victory over Schalke.
'Sheasy' said he was calling time on his playing days this week as his current club Reading end their campaign this weekend against Birmingham City.
“He was one of the guys who really helped me when I came to United,” Smalling told us. “I was blessed to have Rio [Ferdinand], Vida [Nemanja Vidic], Sheasy and Jonny [Evans]. All experienced players when I came here.