"I've been optimistic. I was optimistic last week about Elvis, too, so we'll see where we're at by the end of the week," Harbaugh said Thursday.
Dumervil sprained his left ankle in Baltimore's Thanksgiving win over the Steelers and returned to the contest. But he didn't practice the entire following week and was inactive against the Vikings.
However, Dumervil said he's making progress and seemed hopeful that he'll be able to play Monday in Detroit.
"It's definitely gotten better. The strength is getting there," he said. "I'm just working, just trying to continue to work on my conditioning and really strengthen that ankle to get me to a point where I can tolerate it. ...
"It's kind of an unusual ankle sprain - it's sort of a bruise/sprain, so that's why I was going to the doctor. You feel things in different areas, but I do feel better. So there's no doubt about that."
Does Dumervil think he'll be able to practice unlike a week ago?
"I'm going to try to go out tomorrow, just get out with the guys and get some work in. That's a good team in Detroit," he said.
The 29-year-old has 9.5 sacks in 12 games this season. He doesn't seem to regret that he returned to the game against the Steelers on Nov. 28 after suffering the injury in the first half.
"When you're out there playing, you've just got to go out and help the team win. Man, it hurt," Dumervil said. "But we got the W. I feel good about that. So I just want to make sure the next time I'm out there that I can be effective."
Update: Dumervil was the only member of the team to sit out practice Thursday. Safety Brynden Trawick (ankle) was a limited participant, but returned to practice after missing the last two games. Cornerback Lardarius Webb (abs) was also limited.