The Shrimpers were beaten 3-1 at Roots Hall by AFC Wimbledon on Tuesday night, leaving the club six points off the play-off spots with nine games left.
And stand-in skipper Clohessy - who had given his side the lead from the penalty spot against the Dons - believes another home defeat at the weekend against struggling Torquay would end their hopes of making the top seven.
"If we don't win on Saturday then we won't make the play-offs," he told the Southend Echo. "We need seven wins from nine games to get back in there and we can't afford to lose against Torquay.
"We need to start picking up more points at home too because if we had done better at Roots Hall this season I think we'd be cruising at the top of the league.
"I don't know why we don't do better at home but a few ideas are being bandied around the dressing room. It's a bit of a worry if I'm honest but we weren't good enough against Wimbledon and that was our fault.
"It wasn't down to the gaffer or (assistant) Graham Coughlan, it was down to the players because we just weren't at the races."
- Sports & Recreation