Striker blow for Huddersfield Town plus Darren Moore's thoughts on next Championship opponents Sunderland
Harratt came off in clear discomfort with a hamstring issue after just 21 minutes against the Saints.
Moore confirmed that David Kasumu and Delano Burgzorg have had no side-effects – both made their returns from injury at the weekend – and are available for the encounter at the Stadium of Light.
Moore, whose Town side have won just once in ten outings under his watch, said: "With the game being Wednesday night, it gives us an extra 24 hours, so we're giving all the players an assessment tomorrow (Wednesday).
"But Kian Harratt won't be available, he's got a muscular injury. We'll know more on his timeframe later on today or tomorrow because we're still waiting for some of the medical reports to come back.
"David Kasumu and Delano Burgzorg came through the other day with no issues and should be able to be involved again tomorrow.
"We want everyone back as soon as we can, but Maxy (Chris Maxwell) has demonstrated that although we see Lee as the number one, given the opportunity he can step in and perform very very well.
"It's a great testament to him that he's always ready when called upon and he wants to compete with Lee for that number one spot."
Town face a Sunderland side who are in the play-off mix, but smarting after a 2-0 weekend loss at Plymouth.
The Black Cats have fared better on home soil of late and have won their last two matches on Wearside, against Norwich and Birmingham, by 3-1 margins.
Moore added: "At home they're a very strong team and very fluid with the attacking options they've got.
"Whoever they go with, it's the same outcome with how fluid and effective they are. They've got the home record they've got because they're very effective at what they do.
"Myself and the players are looking forward to the challenge. We know we have to keep adding to our game and improve week in week out and get that understanding between the players. We have to come together as a group and face it together."