SANTA CLARA (AP) — Vance McDonald has been fortunate to spend his rookie summer as the understudy to veteran San Francisco tight end Vernon Davis, who has been eager to take McDonald on as a little brother and teammate, to guide him through the rigors of training camp and the regular season.

McDonald is doing plenty of prep on his own, too. He regularly falls asleep with the 49ers’ offensive playbook right within reach — a book he knew would be thick yet has surprised him with just how expansive it is.

“Let’s just say I heard them say how big it was and I said, ‘Ah, it can’t be that bad,’” McDonald said, smiling. “And I just stared at it the first time and I was just like, ‘Wow.’ It’s extremely extensive but that’s kind of what it takes to be successful, so that’s what I’ve got to do to get it done.”

The 49ers traded up with Green Bay to draft McDonald out of Rice with the 55th overall selection in the second round of April’s draft, and he showed promise in his preseason debut. McDonald made four receptions for 66 yards, including a 21-yard gain, and was targeted eight times in San Francisco’s 10-6 exhibition loss to the Denver Broncos on Thursday night.

Offensive coordinator Greg Roman thought McDonald took a nice step in his first game, while also wishing he had converted a couple of the balls he missed — one an obvious drop.

“Liked the look in his eye before the game,” Roman said.

Yet McDonald will sit out Friday’s game at Kansas City nursing an undisclosed injury. Coach Jim Harbaugh said he likely would be sidelined between seven and 10 days without providing further details.

“He’s working through a little something this week, better to be cautious,” Harbaugh said Monday. “Everybody has high hopes and expectations for Vance. He’s done a very good job.”

It hasn’t been easy getting used to the pace or workload, yet McDonald points to a moment during organized team activities when he received positive feedback from the coaches about the strides he had made being more aware of what was happening from snap to snap.

“They could see a point when it went from that, ‘Oh, man,’ first glance, hesitant, to just instinctive,” McDonald said. “They could kind of see that switch flip on. I don’t know exactly when that was but I certainly feel now that it’s a lot more natural going with the offense in terms of what your job is each play.”

Davis has enjoyed doing a little bit of teaching and mentoring with McDonald, a physical specimen at 6-foot-4 and 267 pounds. And, going with Harbaugh’s regular refrain of not making comparisons, Davis wants McDonald to develop his own style — defensive lineman Justin Smith is already impressed with McDonald’s hands and how he “catches the ball away from his body, really good possession tight end.”

Davis told McDonald he could become one of the talented tight ends in the NFL, topping even Davis’ accomplishments one day.

“He’s just one of those guys when he walks in the room, he brightens the room up. That’s what I love about him. He’s a big dude, he’s humble, he works. He wants to be the best tight end,” Davis said. “You look at it, a guy like Vance might come in here and be like, ‘Vernon Davis this, Vernon Davis that, he’s fast, he’s strong.’ Everybody’s different. Jason Witten is not as fast as me, but he’s still one of the best tight ends out there. Tony Gonzalez is not as fast as me and he’s still one of the best. Every one of us, we all have different tricks, and that’s what I’m trying to get Vance to get, ‘Vance, don’t be discouraged by what I’m doing, do your own thing and be better, be great, because you could be better than me in different ways. Use your own craft and your own God-given ability and put it to work.’”

McDonald — from the tiny town of Winnie, Texas — realizes just how tough a job he has following not only Davis but departed second tight end Delanie Walker, who had 21 catches for 344 yards and three touchdowns last season and is now with the Tennessee Titans.

“Watching film with Delanie, that’s a lot to fill,” McDonald said. “He was a deep threat, he could get it done interior inside, too. That’s a big void that the second tight end guy has got to come in and fill. It’s still just a day-by-day thing, you’re taking techniques and doing everything the coaches tell you. I might not be as fast as Delanie was but I certainly hope to say that I can use technique to get open.”

That has been an adjustment in itself from college football to the pros. Most notably the finesse and how players use their hands more and not just positioning with their bodies.

The transition has been daunting at times.

“You’ve got to be smooth and quick,” McDonald said. “It’s just a different game. It’s all about adapting.”