Just four points clear of the drop zone, the under-performing pair come into the game on the back of contrasting results, as the hosts enjoyed a special success last time out, while their visitors failed to win either of their two fixtures in the past week.
Match preview
After a difficult spell in which they crashed out of continental competition and picked up just one Campeonato Brasileiro point from a possible six, Internacional travelled to Rio de Janeiro last week more in hope than in expectation. Returning to base, then, with three points in their pocket following a 4-0 defeat of defending champions Flamengo was more than head coach Diego Aguirre could have dreamed of.
Already two goals to the good before the hosts' star striker Gabriel Barbosa was red-carded just after the hour mark, Inter went on to add another pair - including Yuri Alberto's hat-trick strike in the 70th minute - to stun the high-flying Rubo-Negro at the Maracana.
As they finished close runners-up to Flamengo last season, expectations remain high at the Porto Alegre-based club, but a sluggish start domestically was recently compounded when they were eliminated from the Copa Libertadores on penalties by Fla's current quarter-final opponents Olimpia.
Not only that, but ahead of Fluminense's visit, they have earned just six points as hosts this season, leaving them looking over their shoulders rather than peering confidently upwards at the continental qualification places.
Once in charge of the club for a spell six years ago, Aguirre returned to the Inter dugout following the departure of Miguel Angel Ramirez earlier this season, but is only now seeing light at the end of the tunnel. His side will hope that precedent is rendered meaningless on Sunday, though, as their visitors have beaten them in three of their last four encounters.
In contrast to Internacional, last month, Fluminense progressed from the Copa Libertadores last-16; winning 3-0 on aggregate against Paraguay's Cerro Porteno.
However, since then, the Rio club have suffered a third successive league loss, to America Mineiro, seeing them slip down to 12th in the table - just behind this week's opponents.
Eliminated at the quarter-final stage of South America's premier club competition on each of their last two appearances, they have at least kept themselves in with a shout of progressing to the final four this time, after responding to their domestic woes by holding Barcelona de Guayaquil to a 2-2 draw in midweek.
That first-leg result - salvaged by veteran striker Fred's stoppage-time penalty - could prove the catalyst for improvement back in the Brasileiro, though Flu may well have one eye on the return match in Ecuador next Friday.
Despite their recent travails, head coach Roger Machado will still be seeking to replicate last term's top-five finish come the end of the season, so will hope that his club's recent supremacy over Inter continues on Sunday. A 2-1 win the last time they visited Estadio Beira-Rio, last November, would provide the perfect template for a side struggling to balance the demands of league and cup campaigns.
Internacional Brasileiro form:
Internacional form (all competitions):
Fluminense Brasileiro form:
Fluminense form (all competitions):
Team News
Internacional's previous problems in attack significantly abated last week, as Yuri Alberto returned from suspension to bag a hat-trick versus Flamengo, while Peruvian centre-forward Paolo Guerrero returned from a knee injury to feature on the bench. The former is set to start up front for the home side again on Sunday, with the latter playing a cameo role late on.
However, Ze Gabriel is once more ruled out with a thigh problem and Gabriel Boschilia is struggling with a knee injury which will keep him sidelined. Left-back Moises is back after a ban, though, so should come into the back four in place of young Paulo Victor, who deputised last week.
Fluminense, meanwhile, remain without on-loan striker Caio Paulista, as he is set to miss out again with a thigh strain, while centre-back Nino recently won an Olympic gold medal with Brazil and is not expected to feature, having just returned from Tokyo.
Paraguayan forward Raul Bobadilla had just got over a calf injury before testing positive for COVID-19 last week, so will remain in self-isolation, leaving 20-year-old Luiz Henrique to support former national team striker Fred up front.
Due to their hectic trans-continental schedule, Roger Machado could make changes, with veteran midfielders Ganso and Nene both vying for a start in Porto Alegre.
Internacional possible starting lineup:
Daniel; Moises, Mendez, Cuesta, Saravia; Dourado, Lindoso; Edenilson, Taison, Patrick; Alberto
Fluminense possible starting lineup:
Marcos; Xavier, Claro, Manoel, Egidio; Yago, Martinelli; Kayky, Nene, Lucca; Fred
We say: Internacional 2-1 Fluminense
Though Fluminense have re-found their confidence in the final third, their forthcoming quarter-final second leg against Barcelona looms large, as the prospect of a Copa Libertadores semi-final spot becomes all the more real.
Naturally, their focus has drifted towards a trophy the club has never lifted before, and the visitors' resulting tail-off in league form should continue on Sunday - with Inter poised to take full advantage, having shocked Serie A with their spectacular win last week.