A setback in his knee rehabilitation means the Orioles could be without star third baseman Manny Machado at the outset of the season. (Gene J. Puskar/AP)

Baltimore Orioles third baseman Manny Machado, who is rehabilitating from left knee surgery in October, has not run in five days because of discomfort caused by the breaking up of scar tissue — a setback that makes an already optimistic return by opening day seem even more tenuous.

“Certainly, it looks [like opening day is out]. I’m not there yet,” Orioles Manager Buck Showalter said Saturday. “I’m not going to throw that wet blanket over that yet. I know Manny’s not.”

Showalter said although it might seem ominous, the delay in running is a precautionary measure and something that can occur with these types of surgeries. He added that Machado seemed to be in good spirits Saturday morning and that he could be “back in the flow” of his rehab program in the next few days.

“The way I understand it, it’s scar tissue that flared up and got a little sore and we decided not to push it, which is what we talked about all along,” Showalter said. “We are not going to push it to the point where it ends up being something. We want to resolve this. The trainers have talked to the doctors, you expect that [scar tissue release]. The surgery side, the knee and everything, feels great. That’s been the most encouraging part.”

Machado had surgery Oct. 14 and at the time the recovery period was considered between four and six months. The end of that spectrum takes him into mid-April. Machado and the Orioles have said throughout the process that they won’t rush him back even if it means missing the first few weeks of the season, which begins for the Orioles on March 31 at Camden Yards against the Boston Red Sox.

Although the Orioles still aren’t ruling out opening day, Machado was hoping to be re-evaluated by his surgeon, Neal ElAttrache, this week.

Yoon finally makes debut

After dealing with a month of uncertainty, a new team on a new continent, and plenty of work visa-related hoops to jump through, South Korean right-hander Suk-min Yoon finally made his Orioles debut.

It lasted 11 pitches.

“I knew I’d be nervous, but I pitched nine years in Korea, so overall I wasn’t as nervous as I thought I’d be,” said Yoon, who signed a three-year, $5.75 million deal in mid-February but couldn’t pitch stateside until securing his work visa in Canada last week. “I waited a long time to throw, so overall, I’m relieved. I’ve been working hard for this day to come.”

Yoon’s first pitch was clocked at 91 mph on the stadium radar gun, whose recordings always seem a little exaggerated, but it gave Yoon some confidence.

“I was amped,” he said through interpreter Justin Yoon. “I honestly thought I was going to throw about 88, but once I saw the 91, I felt good.”

His second pitch was smacked for a single by Yankees farmhand Ramon Flores. Yoon then induced two flyballs and a groundout. The 27-year-old threw only three balls in the outing, an eventual 2-1 Orioles win. . . .

Right-hander Chris Tillman turned in the longest outing of the spring for an Orioles pitcher Saturday as the Orioles beat a makeshift Yankees team.

Tillman, the likely favorite to start opening day, threw five scoreless innings before giving up a homer to Francisco Arcia to begin the sixth. It was the only run and just the third hit allowed by Tillman. . . . Catcher Matt Wieters, who has a sore right ankle, said he expects to play Monday.