He aggravated the knee injury during practice Thursday and didn't practice Friday. He was then ruled out for Sunday night's game against the Buffalo Bills.
"It wasn't a setback," said Smith-Schuster, who also said he doesn't have a timetable for his return. "You know, just more so like I pushed myself too hard where I gotta slow myself down. I'm so competitive, just to get out there and be great. I gotta take it slow."
Smith-Schuster returned to practice Wednesday as a full participant for the first time since being injured, but he left early on Thursday and was listed as a limited participant in the team's official injury report.
Smith-Schuster has missed the past three games with the knee injury -- which he characterized as a "noncontact" injury -- and had been eyeing a return Sunday night. He only returned to running in a straight line on Dec. 4.
Having to scale back this week because of aggravation was a wake-up call for the receiver.
"When you go too hard every day, you kind of get that moment like, yeah, you've got to slow yourself down in order to get wherever you want to get to," he said.
On Thursday, offensive coordinator Randy Fichtner was still optimistic about Smith-Schuster's return, adding that the third-year receiver was eager to get back on the field.
"He was wanting to get back last week," Fichtner said. "You know, injuries. He's got all the enthusiasm and energy and effort and want to. You know, sometimes injuries take their own time. You've just got to keep working through it."
"I've never been in a situation like this where I've been out for a long period of time," said Smith-Schuster, adding he didn't initially know he suffered the knee injury. "Just kind of week by week. It's something that's definitely new to me. I'm learning myself and how I react to it. It can be frustrating sometimes. But at the same time, it's just a part of life, it's a part of the game. Just what comes with our job."
For Smith-Schuster, the key to recovering is increasing strength in his leg.
Conner has an injury to the AC joint in his shoulder. He was a full participant in practice on Wednesday and Thursday, and listed as questionable on Friday.
In the absence of Smith-Schuster and Conner, the Steelers have turned to a committee of offensive skill players to fill their roles. Wide receivers Diontae Johnson and James Washington stepped up in the past two weeks, and in the running game against the Arizona Cardinals, the Steelers deployed four different backs.
"They've been snapping out there all week, this past weekend, just doing their job," Smith-Schuster said. "It's amazing to see how far we've come with the guys that we have on the field."
The Steelers (8-5) are on a three-game win streak without Conner and Smith-Schuster, but coach Mike Tomlin was blunt and succinct during his Tuesday news conference when asked how much the offense needed the pair of playmakers.
"A lot," he said.