OWINGS MILLS - Ravens starting defensive tackle Arthur Jones was ruled out of Thursday's game against the Denver Broncos on Monday, and it's unclear when Jones will be able to return to the field.
Jones hasn't practiced since Baltimore's third preseason game two weeks ago because of a non-football health issue.
Ravens coach John Harbaugh has declined to specify what the health issue is, but he said Tuesday that Baltimore is unsure when Jones will be able to get back to football.
"Like I said last week, I'd rather leave an explanation of Art's situation up to Art," Harbaugh said. "It's not anything life-threatening or anything like that, but it's non-football related. We've just got to get some tests done to make sure he's OK. And until the tests come out the right way, he's not going to be able to play.
"It's something that I've been told now that they can't tell you how long it'll be. It could be a week. It could be indefinitely. We don't think it's going to be the second part of it, but he's going to see a specialist here on Wednesday."
Jones hasn't been available to the media since the issue first came about, but he posted something on Twitter Tuesday afternoon.
"As many of you know I'm having personal health issues," Jones said. "Please respect my privacy. We as athlete's go through real life problems also. Thank you all for your love and support. Ravens fans are the best!! See you all on the field soon!!!"
With Jones sidelined, Marcus Spears will likely get the start at defensive tackle against the Broncos Thursday.
Spears signed with Baltimore during the spring after spending the first eight seasons of his career with the Dallas Cowboys.
He started six games for the Cowboys last season.
He missed time earlier this summer with a hamstring injury, but he returned to practice two weeks and hasn't missed any time since.
"Marcus has been around," Harbaugh said. "He's in great shape. He's practiced well since he got over the hamstring. He really looks good, and he's ready to go."