SANTA CLARA, Calif. -- When it comes to tight ends, there is little doubt the San Francisco 49ers miss their best, Vernon Davis, who continues to miss minicamp while holding out for a new contract.

However, his absence is allowing wide receivers to take some of the June spotlight.

Rookie fourth-round pick Bruce Ellington, second-year player Quinton Patton and veteran Brandon Lloyd are highlighting a passing attack that will be heavily scrutinized in 2014. San Francisco's passing game ranked 30th in the league last season, and it couldn't come through late in postseason games that ended their last two deep runs in the playoffs.

For the 49ers, who use a lot of two-tight-end sets and often face eight-man fronts, there is a need to find ways to spread out defenses to get more room to run.

By adding Ellington, Lloyd and Stevie Jonhson -- who has worked sparingly in individual drills this offseason -- the 49ers hope they can force defenses to play more honestly, creating space for the running game.

With Davis gone, tight ends Vance McDonald and Garrett Celek are receiving the majority of reps with the first-team offense, while Derek Carrier, Asante Cleveland and Kevin Greene are working with the reserves. McDonald, a second-round pick in last year's draft, appears to have the upper hand on returning as the team's No. 2 tight end.

However, it hasn't been a great camp for McDonald to this point. He continues to drop more passes than he should. He made just eight grabs for 119 yards in his rookie season.

On the other side of the ball, the 49ers have an interesting battle to replace All-Pro inside linebacker NaVorro Bowman, who sustained an ACL tear in the NFC Championship Game in Seattle. Bowman continues to show improvement during his rehab, but it is clear the 49ers are in no rush to get him back on the field before he is ready.

Michael Wilhoite and rookie third-rounder Chris Borland are competing to replace Bowman at least through the first six weeks of the season. Borland is displaying his instincts during camp, and he was praised by coach Jim Harbaugh for his ability in coverage despite having short arms and less-than-ideal speed.

The former Wisconsin Badger was the Big Ten defensive player of the year last season, and he forced 15 fumbles throughout his career, good for second all-time in Football Bowl Subdivision history. However, his arms measured just 29 1/4 inches, and he runs a 4.83 40-yard dash. His college production was first-round worthy; the question is whether he will have the physical tools to measure up in the NFL.

Wilhoite went undrafted out of Washburn University as a safety, and he converted to linebacker with the 49ers before becoming a key cog on special teams. He stepped in for Patrick Willis during brief spells last season while the star linebacker was out due to hand and groin injuries, and Wilhoite played well alongside Bowman.

However, with Bowman on the shelf, Willis is moving to the Mike linebacker role after playing mostly Jack last season.

--Starting right guard Alex Boone is holding out with two years remaining on his deal, forcing the 49ers to go with a new look on the right side of the offensive line. Newcomer Jonathan Martin -- who was subject of last season's bullying scandal with the Miami Dolphins -- and Joe Looney are manning the right tackle and guard spots, respectively.

Looney is the favorite to replace Boone should Boone's holdout bleed into training camp, while Martin is in for Anthony Davis, who had offseason shoulder surgery. Davis is expected to return for the start of training camp.

NOTES: Coach Jim Harbaugh confirmed that DT Justin Smith had a procedure to fix something this offseason, but he wouldn't provide specifics, saying only that Smith was not cleared to participate fully in practice yet. Smith was on the side working out with other rehabbing players including S Jimmie Ward, CB Keith Reaser, S C.J. Spillman, WR Jon Baldwin, FB Trey Millard and NT Ian Williams.