The 22-year-old striker, who joined the Shrimpers on loan in January, was released by Wolves on Thursday and does not have a contract at any other club lined up.
Cassidy admits he did not deserve a new deal at Wolves and hopes to prove his credentials when he turns out for Southend in the first-leg against Stevenage, live on Sky Sports 1HD on Sunday.
He told Sky Sports: “It’s obviously disappointing to be released but these things happen in football. I understand it. I’ve not done as well as I’ve wanted at Wolves and I don’t think I deserve the contract.
“There haven’t been any discussions with Southend or any other club yet over a contract but obviously, once the season is done, I’m ready to listen offers from whoever. So this is the opportunity to prove myself with a few weeks to go until the summer. These play-off matches are massive.”
Southend missed out on automatic promotion with defeat to Morecambe on the final day – but Cassidy, who has impressed in 17 appearances since his arrival, insists the disappointment is firmly behind them.
“We need to regroup and put things right and the mood in the camp to do that is good. We’ve had a good run of form and that defeat is already behind us,” he said.
“We’ve had a normal week but with a big carrot dangled in-front of us at the end. Everyone’s been training well and we’re full of confidence. We’re focused and know the task in hand.”
Although technically without a club, former Wales U21 international Cassidy remains calm about his future and believes his spell in League Two has been vital for his development.
“In pre-season last summer I don’t think I had a fair shot at Wolves. I was training with the U21s,” he said.
“Under Stale Solbakken he never really looked beyond the first team. I came back in when Dean Saunders took over and played in eight Championship games, but then under Kenny Jackett it never really happened for me.
“Moving down to League Two has been a brilliant learning curve. It’s physically demanding and tough, but still technically good so I’ve improved on different aspects of the game that I might not have higher up the leagues.
“As much as don’t like moving around so much, I appreciate the loan has made me better. But the next contract I sign I hope allows me to settle somewhere and kick on in my career.”
Stevenage v Southend, League Two play-off semi-final first-leg, Sunday May 10, Sky Sports 1HD, 6.30pm