While Casswell has been talking down the prospect of another trip to Wembley, others at the club have been talking about nothing else since Tuesday's third qualifying-round replay victory against Brackley Town.
Leek famously made it all the way to the final in 1990 after beating the likes of Conference teams Telford, Darlington and Stafford Rangers, only to lose 3-0 to Barrow at Wembley.
But after wins over Evesham United, Witton Albion and Brackley Town, Blues are now into the first-round proper.
However, Casswell admits he's not looking any further than the match at Altrincham.
"It's great for the supporters be talking about Wembley again, it was such a great occasion for the club, but it's not something I've given a lot of thought to.
"There's a long way to go. We are only at the first-round stage. If we win tomorrow, there are another three games before we get to the semi-finals."
Casswell was full of praise for his players after the win against a Brackley side who became television stars when knocking Gillingham out of the FA Cup on their own ground two weeks ago.
John Johnston put Blues ahead on 38 minutes, only for Owen Story to net an 83rd-minute equaliser. Substitute Dan Shelley netted Leek's winner in extra-time.
"It was a great night for the club against a very good team," Casswell added. "They are riding high in Conference North, so for us to hold them to a 0-0 draw at their place and then beat them on our own turf was a fantastic achievement."
Now Casswell wants his players to take that high level of performance into tomorrow's game at Moss Lane.
"If we can produce the kind of football we did against Brackley then we will give Altrincham a good game. They are favourites, but we may just surprise them."
The Robins are second in Skrill Conference North, two levels above Leek in the league pyramid, and level on points with leaders Hednesford Town. They are managed by former Port Vale boss Lee Sinnott.
The 48-year-old had a disastrous spell in charge of Vale after joining them from Farsley Celtic in 2007. He was sacked the following September after just nine wins in his 44 games in charge. Now Sinnott is plotting a course into the Conference Premier with the team he joined in May 2011, but he knows they will be in for a battle tomorrow.
"We have had Leek watched and there is no question we are in for a tough test," he said.
"They are going really well in their league (top of Evo-Stik Division One South) and have followed up a draw at Brackley by beating them in the replay.
"That tells you what we will be up against. We will have to be on our game."
Former Leek striker James Walshaw will be leading the line for Altrincham, and with 14 goals to his name, Sinnott knows how important his contribution could be.
He added: "He dispatches his goals well. You can tell from open play, as well as from the penalty spot, he's a confident lad. He has that one-dimensional thought process all top strikers have. If he's near goal he wants to get a shot away."
Walshaw had a brief spell with Blues in 2008 before leaving for Farsley Celtic.
Casswell, too, has his sharp-shooter at the ready. Jordan Johnson, with 22 goals, will start up front tomorrow before starting a suspension after being sent off in Leek's recent game against Eastwood Town.
Casswell said: "Jordan is an important player for us. He not only scores from open play, but can also take a great free-kick.
"But tomorrow is not about one player, it's what the other players around him do."
Andy Bratt and Ryan Dicker should be fit to return after illness. Dicker pulled out of Tuesday's game, while Bratt lasted just nine minutes.
Leek banked £4,000 from their victory over Brackley to make it £10,000 won in the competition so far and another £5,000 is up for grabs with victory tomorrow.