Nigel Adkins confirmed in his pre-match press conference that Long will replace first-choice goalkeeper David Marshall between the posts as the Tigers take a break from Sky Bet Championship action.
And the 25-year-old custodian – whose only appearance this season following his summer switch from Sheffield United came in the Carabao Cup defeat to Derby County in August – is looking forward to being back out on the pitch.
“I’m excited to play on Sunday,” he said. “It’s an opportunity to get a run out having not had too many chances to impress so far this season.
“It can be a tough situation being a number two goalkeeper at any club. But, I always make sure I’m ready to play whenever I’m called upon because you never know when the next opportunity to play is going to come along.
“I’ve focused on developing and improving in training day in, day out and I just want to go out and show what I can do and what I’ve been working on throughout the season at Millwall.”
The Tigers drew 2-2 when visiting Millwall in the league five weeks ago but will come up against an opponent – like themselves – in a rich vein of form.
Neil Harris’ side have won their last three league fixtures against Reading, Nottingham Forest and Ipswich and Long is under no illusions about the challenge facing him and his team-mates at The Den.
“It’s quite a remarkable run we’ve been on to be fair – which has been the result of a lot of hard work and graft. I’m delighted for the gaffer and the backroom staff.
“Obviously the lads have been brilliant as well. We’re looking up in the table right now and we want to continue our league form in the FA Cup.
“We know what type of test we’re going to face at Millwall – it’s a tough place to go at any stage of the season.
“We know what we’ll come up against though. They’ll look to put balls into the box and put us under pressure.
“It’s going to be a competitive game but we just need to stick to the qualities we’ve got as a team and continue to play our way.
“I’m sure both sides will make changes for the game, but hopefully we can keep our momentum going and get a result that sees us involved in the draw for the next round.”