The O’s come into the game on the back of a hard-fought 2-2 draw away at Wrexham AFC last week.
Chris Holroyd put the Welsh side ahead within the first minute but Macauley Bonne equalised in the 23rd minute.
Holroyd gave the home side the lead for a second time but once again the O’s managed to pull level, this time through Mark Ellis’ 85th minute header.
Gillingham have had a difficult start to the season and sit within the League One relegation zone after 16 matches.
However, the Gills have won two of their previous four matches under caretaker manager Steve Lovell, beating Rotherham United 3-1 on Saturday.
Josh Parker opened the scoring in the 2nd minute, before top-scorer Tom Eaves doubled the advantage just before half time. Kieffer Moore pulled a goal back for the home side but Parker scored again to secure all three points.
Zain Westbrooke made his first start for the O’s in Saturday’s draw and having impressed will be hoping to keep his spot in the starting line-up, while Joe Widdowson and Alex Lawless are both pushing for a return having overcome respective hamstring and groin injuries.
Forward Matt Harrold completed an hour for an Orient XI in a friendly against Barnet on Tuesday, and will hope to be available for tomorrow’s clash.
However, Steve Davis will once again be without loanees Mark Ellis and James Brophy who have not been given permission by their parent clubs to feature in the FA Cup for the O’s.
IN THE BUILD UP
Head Coach Steve Davis ahead of tomorrow’s encounter – here.
Striker Macauley Bonne reflects on Zimbabwe call-up and looks ahead to Gillingham – here.
The Club has sold 470 tickets ahead of tomorrow’s Emirates FA Cup tie at Gillingham.
Tickets will be available for supporters to purchase from Gillingham tomorrow, with prices as follows:
Concessions (65 and over & Under 18)
Supporters collecting tickets at the Priestfield Stadium tomorrow will be able to do so at the Ticket Office.
Can’t make the game? Follow live updates through the official Twitter feed, or listen to audio commentary from Dulcet Dave on Ozone.
Audio commentary will be available through the match centre which will appear at the top of the leytonorient.com homepage, with commentary starting 30 minutes before kick-off.
Match report and reaction following the game will appear on leytonorient.com.