Blues will start favourites at home to the Midland Alliance side in tomorrow's second qualifying round, but Casswell expects a tough game against a Bridgnorth side who are unbeaten this season.
What's more, the Shropshire outfit beat Rushall Olympic in the last round who play a league above Blues.
Now Casswell is demanding his team don't let their standards drop as they look to follow up their 5-0 win over Bewdley in the last round.
He said: "We know this is going to be a difficult game and we certainly won't be taking anything for granted.
"Our attitude was spot on against Bewdley. We have to be able to come in after this game knowing we have done everything we can."
Casswell welcomes back midfielder Sam Hall and striker Peter Wright after both missed Saturday's 2-1 win at Warrington in the FA Trophy.
However, striker Tim Grice is a doubt after aggravating a hamstring problem at Warrington.
Former Southport hit-man Wright is already looking an inspired signing after scoring four goals in his opening two games.
The 30-year-old was plucked from the contact book of Leek's general manager of football Pete Ward, the experienced operator who joined the backroom staff at Harrison Park after he was axed as Kidsgrove manager at the end of last season.
Casswell added: "All the credit for Peter Wright goes to Pete Ward.
"Pete is out watching games every night and his knowledge of players at this level, both locally and further afield, is tremendous."
However, Casswell says the recruitment of Wright doesn't mean he's writing off last season's goal-hero Grice.
He said: "We felt as though we needed another striker to give us competition for places.
"Peter has started scoring straight away. He's a clever player, who has scored goals at a higher level and has done brilliantly so far, but it's only two games.
"Tim Grice got 21 goals in 23 games to fire us into the play-offs last season. It was always going to be difficult to keep that up, but we are by no means saying he can't do it. I think the hamstring problem hasn't helped."
Meanwhile, Casswell has been delighted with another newcomer, keeper Daniel Lloyd-Weston.
The 21-year-old was recruited a fortnight ago after Danny Roberts was ruled out with a broken finger.
Leek were put in touch with Lloyd-Weston by Neil Baker, their former manager who is now back full-time at Crewe Alexandra as assistant manager.
Former Port Vale academy keeper Lloyd-Weston was also on the books at Cheltenham Town before joining AELK FC in the Greek Football League One.
Casswell believes the Manchester-born youngster can fulfil his ambition to get back into the Football League.
He said: "He's done very well for us and been very composed. "He is ambitious and very keen to get back in the league.
"If he can use us as a stepping stone, then great. Having him here is another string to our bow."