Millwall will be at home to Gillingham in the First Round of the 2018/19 Carabao Cup.
The draw, made in Ho Chi Minh City, Vietnam, on Friday morning paired The Lions with the Sky Bet League One club.
Matches will be played week commencing 13th August.
It will be the first meeting between the two since a 1-1 draw at Priestfield in April 2017. The last time the two clubs played at The Den was in December 2016, as Lee Gregory and Fred Onyedinma were on target in a 2-1 victory.
Full details, including ticket selling arrangements, a date and a kick-off time, will be confirmed in due course.