The 41-year-old hung up his boots in 2008 following a season with Cardiff City.
However, Sinclair is now the current assistant of Lancaster City, who have a number of injury concerns ahead of their FA Cup tie with FC United of Manchester today. As a result, Sinclair has admitted that his services may be required.
"There is a possibility I might have to get involved this weekend because we are struggling for numbers," Sinclair told BBC Sport. "My wife told me to behave myself because I am an old man now. I am touching 42, but I still feel fit and able.
"I still look after myself and the most important thing is I still love the game and I get involved in training when I can. If the gaffer says we are struggling for numbers and asks if I want to play I will, but I don't want to take the opportunity away from one of the young lads."
During his career, Sinclair made 12 appearances for England, four of which came at the 2002 World Cup.