The Liga side host Lyon in the second leg of their encounter on Wednesday night following their 0-0 draw in the first leg on February 19.
Neither player managed to grab the headlines in their initial match at the Lyon Olympic Stadium last month, but they are familiar with one another as both played in Ligue 1 last season.
Malcom departed Bordeaux and the French top flight for Barcelona in the summer, but has struggled to settle in at the club having made just one league start so far this term.
Fekir, meanwhile, has enjoyed another brilliant campaign for Lyon where he has racked up nine goals in 21 league appearances.
He is the club's current top scorer alongside Moussa Dembele and has played a major role in the club’s current standing of third position in the table.
But, despite Malcom’s absence from the Barcelona line-up, the forward insists his team will need to stop Fekir in Wednesday’s game if they are to advance to the last eight.
Barcelona are also on course to win the treble this season, as Ernesto Valverde’s side already hold a seven-point lead at the top of La Liga.
The club are also in the Copa del Rey final scheduled for May, with a Champions League triumph now looking their most difficult of tasks if they are to complete the treble.
"We want to win the hat-trick, we're going to work for it, it's the best team, the best players, Lyon has good players,” Malcom added.
“I think that if we do our job, well, we'll pass."
Barcelona then follow up their midweek clash against Lyon with an away trip to Real Betis in the league.