Given the lack of holes on the roster heading into the offseason, receiver headlines this list because of the loss of one of the team's breakout performers in 2012, Michael Crabtree.
Anquan Boldin figures to slide in Crabtree's role given his similar skill set and ability to make plays in traffic. But the battle for the No. 2 job with Crabtree out remains the most talked about topic in training camp.
Not helping the 49ers was the rash of minor injuries suffered early to Kyle Williams, A.J. Jenkins and Kassim Osgood while Mario Manningham continues to rehab his way back from November's ACL and MCL tears. The prognosis for his return remains in the air while the other three have resumed practicing with mixed results.
Williams, entering his third year in the system, hasn't seen much time in 11-on-11 drills. The team is either comfortable with his knowledge of the scheme, is monitoring his reps given his hamstring, or both.
That makes Jenkins – 2012's first-round selection in the draft – a key name to watch both Thursday and the rest of the preseason. He'll see plenty of snaps and look to build confidence after what was considered a lot year in 2012 as a rookie. He is still looking for his first catch after dropping his only target last year in Week 17's win over Arizona.
Defensive coordinator Vic Fangio has gone to a rotation at free safety so far in training camp, giving days of first-team reps to Craig Dahl, C.J. Spillman, Trenton Robinson and top draft choice Eric Reid, in order. Fangio indicated the veteran Dahl will start Thursday's game alongside Donte Whitner and get his chances against Peyton Manning while Spillman, Robinson and Reid will work their way in.
Reid will be the starter at some point. The 49ers are just trying to find out when. And without major contact allowed in training camp, it's been tough to gauge his progress outside of the praise heaped by coaches and players for his work ethic, intelligence and overall physical ability. He'll have his first chance to make a statement or take his lumps Thursday. It's safe to assume he'll get more reps than any other free safety.
There's also a chance Reid could work at strong safety opposite Spillman or Robinson as he has in camp when not getting first-team looks with Whitner.
A reasonable argument can be made for the potentially season-ending ACL tear to Chris Culliver being of higher consequence than Crabtree's Achilles. Culliver played poorly in the Super Bowl, but that shouldn't overshadow how good he was in the regular season.
Culliver allowed just 36 receptions on 73 targets, leading the team in cover snaps per reception in just his second year. Quarterbacks had a 76.9 rating while throwing to the receiver he was covering, which was second to Tarell Brown's 75.2.
Tramaine Brock has been the front-runner to replace Culliver and will be one of the most dissected players in the preseason. He'll have Nnamdi Asomugha looking to overtake him and resurrect his career after two disastrous seasons in Philadelphia.
Asomugha has shown flashes of player he once was, especially in man-to-man situations this summer. But without any guarantees in his minimal one-year, $1.35 million deal, San Francisco has nothing to lose if he doesn't make the team.
Seventh-round pick Marcus Cooper has been making strides since the open of camp after not starting a single game at Rutgers and figures play a lot in Thursday night's game to see if he garner practice squad consideration. Other corners looking to improve their standing are Perrish Cox and undrafted free agents Lowell Rose and Darryl Morris.
Ian Williams has made a strong impression in training camp, backing up the two-year contract extension he signed in the offseason after being active in just five regular season games in the last two years. Now, he's slated as team's top nose tackle, making the 49ers look good for bringing him in as an undrafted free agent in 2011.
Fans looking for a sneak peak at what Williams can provide should have a keen eye on No. 93 early in the game in base situations. He has been a disruptor in camp and thrived exploding off the snap and leveraging interior linemen into the backfield early in the play.
Divens is a player toeing the cut line early and will have to have a very good showing in the preseason to supplant Tukuafu and Dobbs, who Harbaugh has used in jumbo packages on offense. Dobbs and Tukuafu are the only remaining players in camp wearing black practice jerseys indicating their use on both sides of the ball.
On Wednesday, Harbaugh said the team would value special teams to the point of keeping players on the roster that have no worth on offense or defense. And without contact in practice, it's tough to evaluate special teams play, especially the coverage units.
Players like Raymond "Bubba" Ventrone, Osgood and Dan Skuta have the best chance to make the team purely as core special teamers. And with just 46 players suiting up on game days, their roster spots are incredibly valuable to guys looking to make the team in reserve roles on offense or defense.
Ventrone hasn't gotten a single rep at his listed position of safety in training camp, but could make the team as Andy Lee's personal protector. Osgood is a former Pro Bowler and All-Pro gunner in punt and kickoff coverage. Should he make the team, that would change the shape of the receiving corps in a significant way. The same goes for Skuta,an outside linebacker who could be battling Parys Haralson for a roster spot given the likelihood third-round pick Corey Lemonier makes the team.
*Statistics from Pro Football Focus were used in this story*