The Sky Blues are three points off the play-off places with seven games left and travel to Fratton Park to face a Pompey side who are eight points adrift of safety, but have lost just one of their last five games.
And Pressley knows his side will have to be at their best to keep their top-six hopes alive.
"It is always difficult playing sides who are fighting for their lives as they have so much to play for," he told the club's official website.
"They will be determined to get the win and we need to be bringing our best game to Fratton Park this weekend.
"They are similar to Hartlepool in that sense and we saw how difficult that game was, so we need the same commitment again.
"Every single day here we train to win, and I will be expecting that mentality to come through on the pitch this weekend.
"We need to be able to keep the momentum up and with us just three points outside the play-offs, there is everything to play for.
"I want to create a real winning culture at this football club and you only achieve that by setting standards and then maintaining them."