In-form striker 'JD' knows Southend's headline-maker Freddy Eastwood from his days at West Ham when Eastwood was a trainee in 2002-03.
Eastwood curled home a corker of a free-kick to eliminate Manchester United in the last round and has bagged 11 goals this season.
"We won't underestimate Southend because they are a good side who've got Freddy Eastwood up front," said Jermain, who also has 11 goals to his name this term, six in his last nine.
"I remember Freddy from when he was at West Ham and even then he scored lots of goals and I remember thinking how sharp he looked. He is looking the part at Southend too.
"They will be up for the game. I watched their win over Manchester United and I thought they were excellent.
"We've got to approach it in a professional way because it is a massive game for us. Winning would take us closer to the final and this is in front of another full house at White Hart Lane."
Jermain Defoe points to a familiar face as one reason why we won't underestimate Southend United in Wednesday night's Carling Cup quarter-final.