The Marlins, who are averaging just over 9,000 fans per game, trail the next-worst team, the Tampa Bay Rays, by more than 200,000 in total attendance.
Miami's 2018 attendance is the worst by a major league team since the Expos' final season in Montreal in 2004.
Sunday's home finale likely won't draw big numbers either as the Marlins (61-93) have the worst win-loss record in the National League, and the Reds (66-90) are also a last-place team.
In addition, the Marlins will have to compete with the NFL as the Miami Dolphins -- off to a promising start at 2-0 -- will host the Oakland Raiders on Sunday. The Marlins and the Dolphins are set to start at 1 p.m. ET.
Meanwhile, Marlins CEO Derek Jeter has indicated that manager Don Mattingly will be allowed to return in 2019 to fulfill the final season of his four-year contract.
"Is he going to be back in 2019?" Jeter said when asked. "He's under contract, so yeah."
Jeter, who was used to winning or at least competing for World Series titles during his days as a New York Yankees shortstop, is having to preach patience with this Marlins team.
"Where we are starting from, the only way to go is up," Jeter said. "This is a transitional year for us to learn as much as possible about the organization."
Richards, who has struck 113 batters in 112 2/3 innings, is known for his changeup, which often gets swings and misses down in the zone.
However, he has not won a game since he beat the Philadelphia Phillies on July 14.
In three starts this month, he is 0-2 with an 11.12 ERA.
Meanwhile, Lorenzen broke into the majors in 2015, pitching in 27 games (21 starts) and posting a 4-9 record with a 5.40 ERA.
But Lorenzen was strictly a reliever in 2016, when he posted a 2-1 record and a 2.88 ERA, and again last year (8-4, 4.45 ERA).
This year, Lorenzen was again a reliever for his first 42 appearances, but in his only start, he allowed one hit, one walk and one run (unearned) in four innings against the Milwaukee Brewers on Tuesday.
It was his first start after having made 151 consecutive relief appearances.
"I've been saying, 'Give me a chance! Give me a chance!'" Lorenzen said after his Reds beat the Brewers 3-1. "They gave me a chance against a good lineup, and I was excited. It was like, 'Man, I better step up'."
Lorenzen, 26, did just that, striking out three batters, inducing weak contact and getting Brewers batters to expand the zone.
Lorenzen, a native of Anaheim, Calif., was the 38th overall pick in the 2014 MLB Draft, selected by the Reds out of Cal State Fullerton.
At 6 feet 3, 215 pounds, Lorenzen can muscle up his fastball, which averages an impressive 95 mph.
He has a 2.63 ERA this month overall and a 2.62 ERA on the road for the season -- two trends that could bode well for him Sunday.