Midfielder David Wright, on loan from Crystal Palace, made his debut during the Gills' 4-0 win over Bristol Rovers and looks set to keep his place in the starting line-up on Tuesday.
Allen's men sit at the top of League Two having not lost a game all season, so the manager may be reluctant to make changes to a winning side.
Gillingham's opponents are in fine goalscoring form so Allen may decide to select a more defensive side than the one that started against Bristol Rovers on Saturday.
After a slow start to the season, Southend have gone on a four-game unbeaten run in which they have scored 11 goals.
Their manager Paul Sturrock could be without striker Neil Harris.
Harris missed the Shrimpers' 3-1 win over Cheltenham at the weekend with a knee injury and is a doubt for Tuesday's clash at Priestfield.
Long-term absentees Freddy Eastwood (calf), Luke Prosser (calf) and Ryan Leonard (hamstring) will miss out once again.
Sturrock is confident his side can stun the league-leaders.
"We are starting to climb the league now," he said. "I am very pleased for everybody associated with the club as we have all worked very hard.
"We've had some niggling injuries which have made things hard but everyone has worked tirelessly. We can go and enjoy ourselves and try and peak again like we did against Cheltenham."
- Bristol Rovers