"Not good," he said.
Leyland didn't elaborate, but head athletic trainer Kevin Rand said later that it's right elbow discomfort in the same area Rondon had a few weeks ago.
"He came in today with some complaints of discomfort in his elbow, similar to what he had in Boston," Rand said. "It's hard to determine at this point if it's to that point, so we're just going to treat him today, try to get it quieted down and re-evaluate it.
"The question is: Is it just [out of] going back out there again, getting back up and throwing at 100 percent? Is it that, or is it more than that? We have to obviously err on the side of caution and treat him today with an off-day tomorrow and just kind of re-evaluate it."
Rand did not give a timetable, and he wouldn't say it's day to day. Rand did not, however, use the same outlook as Leyland.
"I would say Jim said not good because he doesn't have him available tonight," Rand said. "It's never good when I walk in [to his office] and tell him you haven't got that guy for tonight."
Even if Rondon feels fine on Friday, it's not clear whether the Tigers would put him back in the bullpen immediately. It's quite possible he won't pitch until next week, which would leave the club to weigh whether he's healthy enough to pitch in the postseason.
Jason Beck is a reporter for MLB.com. Read Beck's Blog and follow him on Twitter @beckjason. This story was not subject to the approval of Major League Baseball or its clubs.