WALTHAM, Mass. – Terry Rozier knows he’ll learn plenty during his rookie season.

Among the lessons?

Speak up when you’ve suffered a potential injury.

The rookie guard, selected by Boston with the 16th overall pick in last June's NBA draft, will miss at least a couple more days with a left knee injury suffered early in training camp, an injury he did not inform Celtics medical officials about until days later.

“It happened the second or third day of training camp,” he said. “I was trying to go for the ball in the paint and I kind of slipped. I didn’t say nothing until we were in Madrid and I saw it start swelling up a bit. Lesson learned. I thought I could just get through it.”

Since the discovery of the injury, Rozier has had his left knee drained which he said was a first for him.

“It’s nothing serious. I just have to be off my feet right now,” he said.

Rozier had some knee issues at Louisville, but this latest setback he says is unrelated.

“It’s not the front of my knee which was an issue in college. It’s the back of my knee that caused the swelling,” Rozier said.

Missing time on the court will slow down the momentum the 6-foot-2 guard was hoping to carry on after a strong stretch of play overseas.

In the first two preseason games, Rozier averaged 11.5 points while shooting 64.3 percent from the field and 64 percent on 3s.  

Since the injury, Rozier has spent time in the swimming pool as well as on an exercise bike. In addition, he has had an earful from the team’s veterans, too.

“You have tell them (team doctors) right away,” Rozier recalled being told by veterans. “Can’t let that happen again; you have to speak up.”

While at Louisville, Rozier tried to tough it out in practice and games when his body wasn’t quite right due to an injury.

“Right now, it’s different,” Rozier said. “Pro level you have to know when to sit out. I’ll be fine. I’ll be out a couple days; nothing big.”