The Gills have only managed one victory in their last six, having also dropped points from winning positions in three out of their last four games. Three points over Plymouth could see them climb from 11th to as high as ninth place, if other results go their way.
Meanwhile, the Pilgrims have also been in poor form of late, having lost six out of their last seven matches. Their promising results in the mid-season faded away, which now leaves them sitting in 18th position.
Gillingham manager Steve Evans has the benefit of no fresh injury concerns going into the game.
Plymouth manager Ryan Lowe is having to deal with a host of injuries coming into this match. Defender Will Aimson is out with an ankle issue, and Jerome Opoku is suspended following being sent off in the 3-1 loss to Sunderland last time out. As a result Ollie Tomlinson will make his first start at centre-back.
The Pilgrims' captain Gary Sawyer, who has been out with an ankle injury since September, will also miss out. The 35-year-old will retire once the season is concluded and take up an ambassadorial role at the club.
Gillingham (4-2-3-1): Bonham - Jackson, Tucker, Cundy, Ogilvie - Dempsey, O'Keefe - Graham, Lee, MacDonald - Oliver.
Plymouth (4-4-2): Cooper - Edwards, Watts, Tomlinson, Law - Camara, Fornah, Grant, Mayor - Hardie, Ennis.
Gillingham have had a frustrating set of results in recent weeks, which has seen them only manage one win in their last six games. That notable 1-0 victory over Peterborough United has been sandwiched in between defeats to play-off chasers Blackpool and Oxford United, as well as draws to bottom half sides Northampton Town and Burton Albion.
Three of their last four have also seen them drop points from winning positions, so they'll be hoping to avoid that on this occasion on Sunday.
Plymouth have also been having a tough time of late, with six defeats in their last seven. This included a 6-0 home thrashing against Charlton Athletic, which led Lowe to describe his side as having "no desire" and "no commitment" in their performance.
Having all been set for a push for the play-offs back in February, they have since lost ten of their last fourteen games to make those hopes disappear. Their last win came against AFC Wimbledon on April 2, so they'll be hoping to add a little gloss on what's been a fairly disappointing season when they travel to Gillingham.
Ones to watch
Vadaine Oliver is undoubtedly the one to watch for Gillingham. The striker has had the season of his career, netting 19 goals in all competitions, and providing a significant presence up front.
His aerial threat is also well-documented, having won 431 duels in the air this season in League One, 140 more than the next highest player. He will be the one the Plymouth defence will need to keep an eye out for on Sunday.
Joe Edwards will be the one to watch for Plymouth. Edwards took on the captaincy in Gary Sawyer's absence, and has provided a dependable presence at right-back for much of the season. He's also managed a career-best nine goals and two assists this season
The last time these two side met was in the reverse fixture back in January, where Plymouth came out 1-0 winners at Home Park. A strike from Luke Jephcott was enough to gain the three points that night.
In the overall head-to-head record, the Pilgrims also edge out in front, having secured 34 victories compared to Gillingham's 30. There have also been 16 occasions where the points have been shared.
How to watch
The game has not been selected for TV coverage in the UK, but an iFollow pass can be purchased for £10 via either club's website to stream the game live.
Kick-off is scheduled for 12:00 BST.