Chen, who's been on the 15-day disabled list with a sprained left elbow since July 24, is expected to return mid-September at the earliest. He's been tossing from limited distances as part of a throwing program, and on Wednesday he made 25 throws from 60 feet.
But the southpaw starter would likely still need to start throwing bullpen sessions and facing live hitters before any talks of pitching in rehab games and rejoining the Marlins began.
"When [his throwing program] originally started, I knew that was the middle of next month at the earliest," Mattingly said of Chen's return. "It's a ways off. It seems like to me there's a long way to go between here and there."
Mattingly said the pain in Chen's elbow that he experienced after his last start on July 20 has subsided, thanks to an injection and extended time off from throwing. But he knows Chen still has a long road ahead of him.
"It's positive from a standpoint that he's doing better and he's on that road," Mattingly said. "But where that gets to, I don't know if that's part of this season."
Mattingly and the rest of the club is just focused on making the playoffs, as Miami entered Saturday night tied with St. Louis for the second National League Wild Card spot. Rosters expand in September, and Chen might not fit into the puzzle down the stretch if and when he returns.
In 19 starts with Miami this year, Chen owns a 5-4 record and a career-worst 4.99 ERA in 110 innings. The 31-year-old averaged more than 175 innings per season over his previous four years with Baltimore.
Patrick Pinak is a reporter for MLB.com based in Miami. This story was not subject to the approval of Major League Baseball or its clubs.