Prior to the match, Frankfurt's sporting director Markus Kroesche revealed that "a club had made contact" regarding Marmoush, with Sky Germany reporting that the forward has already reached an agreement on personal terms with the struggling English champions.
Marmoush found the net in the 32nd minute against his former team, skillfully maneuvering inside the box before sending a shot into the top corner to secure the lead for Frankfurt.
This goal marked Marmoush's 14th in 16 Bundesliga appearances this season, placing him alongside Harry Kane at the top of the scoring leaderboard. The 25-year-old has also contributed eight assists in the league.
“We did plenty to keep a clean sheet today,” said Frankfurt captain Kevin Trapp.
“There’s definitely a few things we can improve on,” the goalkeeper added.
Victory maintained Frankfurt's position in third place, trailing leaders Bayern by six points, who are set to face Borussia Moenchengladbach later on Saturday.
In other matches, Freiburg moved ahead of Borussia Dortmund into sixth place with a 3-2 victory at home against Holstein Kiel, featuring an impressive free-kick from captain Christian Guenter.
Kiel's Nicolai Remberg inadvertently redirected an Eren Dinkci cross into his own goal in the 23rd minute, followed by Guenter's remarkable dipping shot that found the top corner from the right flank.
Freiburg's Vincenzo Grifo added a third goal, although Kiel's Phil Harres made the final moments tense by scoring twice in the last five minutes.
Union Berlin's challenging week continued as they suffered a 2-0 defeat with only ten players against Heidenheim, just days after the German Football Association (DFB) imposed sanctions for fan misconduct.
The DFB ruled that Union's 1-1 home draw against Bochum in December would be recorded as a 2-0 victory for the visitors due to a home fan throwing a lighter at the opposing goalkeeper.
Union president Dirk Zingler criticized the ruling as an "unfair scandal," claiming the court aimed to set a "political example" of the club, which has since appealed the decision.
In the match, Bayern Munich loanee Frans Kraetzig opened the scoring for Heidenheim on a counterattack in the 17th minute during his debut, while Union's Tom Rothe received a red card for a last-man foul. Adrian Beck secured the win for Heidenheim with seven minutes left, marking their first victory since September.
Mainz moved ahead of RB Leipzig into fourth place with a 2-0 home win over Bochum, with Germany international Jonathan Burkardt netting a goal in each half.
Additionally, a 29th-minute goal from Mohamed Amoura led Wolfsburg to a 1-0 victory at Hoffenheim.