O'Connor and Marcelo have left Blues on free transfers for Walsall with contracts at The Bescot until the end of this season.
Blues will recieve an undisclosed fee if the pair can help The Saddlers avoid relegation to Division Two, believed to be around £150,000
O'Connor told the Birmingham Evening Mail: "When a new manager is appointed he can often see what maybe needs to be done as he has a fresh outlook.
"If Steve thinks he has to sacrifice players like myself, Marcelo and, I'm sure, others, then you don't hang around.
"I'm not putting myself or others down, far from it. Hopefully what he does will provide Blues with that extra push to get into the Premiership."
O'Connor will be fondly remembered by Blues' fans for winning the equalising penalty in the League Cup final against Liverpool and then hobbling through extra-time despite injury.
"That day will never, ever go away from me," he admitted.
"We came within a whisker of something great."
"Heart of a Lion, Vision of a Mole" one of the Blues Fanzines once described the ex-skipper.
Never a truer word spoken, he gave his all for our club.
Thanks for the memories Martin and good luck at Walsall!