Despite that fact, he has established himself as an integral part of San Francisco's defensive line, one of the strongest areas of the team and the launching point for the Niners' outstanding rushing defense.
McDonald is one of those hard-working, unheralded players who perform in the background as a rotational player and find themselves on the field in key situations on practically a weekly basis over the course of the season.
McDonald has developed into a solid veteran performer in his four seasons in San Francisco and has found his niche in the team's defensive plan. Lacking great size and bulk for an interior player at the NFL level when he arrived in the league as San Francisco's third-round draft pick in 2007, McDonald has made himself into a solid 290-pounder capable of holding his ground at the point of attack in the trenches.
After an injury-plagued rookie season, McDonald started eight games as a NFL sophomore in 2008, establishing himself as a factor along the team's defensive line.
McDonald settled into a key backup role the next year when the San Francisco defense established a regular starting wall of Isaac Sopoaga at left end, Aubrayo Franklin at nose tackle and Justin Smith at right end.
There is little weakness in that starting unit, and McDonald usually has been the first player off the bench to complement that trio, spending most of his time at left end on base downs and also playing inside on passing downs when the 49ers go to different fronts to facilitate rushing the opposing quarterback.
McDonald finished with no sacks in 2011, but that statistic belied the fact he was one of San Francisco's best at putting pressure on opposing quarterbacks. McDonald ranked second on the team with 26 quarterback hits and was second only to Smith with 56 quarterback pressures last season.
That's a number that won't be taken lightly around the NFL when others consider the worth of McDonald should he hit the open market.
McDonald also ranked 10th on the team in tackles with 57, leading all San Francisco non-starters in that category. That's a number that suggests McDonald played like a starter for the 49ers.
McDonald also displayed his athleticism last year when he recorded the first interception of his career and returned it 31 yards for a touchdown to give the 49ers the lead in their Oct. 24 game at Carolina. It was McDonald's second career touchdown after he returned a fumble 11 yards for a score in 2009. As a special teamer, he also has blocked two field-goal attempts, both of which were returned for touchdowns by the Niners.
With four years of NFL service behind him, McDonald's status as a free agent is in limbo until a new collective bargaining agreement is reached. He would be a restricted free agent under the guidelines used by the league in 2010 free agency.
The McDonald breakdown
2010 performance: Was San Francisco's top reserve along the defensive line and one of the top backups on the entire team who occasionally worked as many snaps as players ahead of him on the depth chart. Was 10th on the team with 57 tackles – leading all San Francisco non-starters in that department – and was one of the Niners' top pass rushers, finishing second on the team with 26 quarterback hits and second with 56 quarterback pressures despite not recording a sack for the first time in his career. Also returned an interception 31 yards for a touchdown in Week 7 at Carolina.
2010 season grade: B-plus
Why he's worth keeping: McDonald has developed into a solid defensive lineman who could be starting material for other NFL teams, and perhaps even for the 49ers down the line. He is a top role player in San Francisco's defensive line rotation and is effective against both the run and pass. He is second only to Pro Bowler Justin Smith among San Francisco defensive linemen in applying heat to the quarterback during passing downs. He is clearly among San Francisco's top dozen defensive players. The 49ers have developed him, and at age 26, McDonald's best years are still ahead of him.
Why he's not worth keeping: At 290 pounds, McDonald lacks the size to be an every-down lineman in San Francisco's 3-4 defensive scheme, and he may command compensation on the open market that approaches starter's money. It would be difficult for the 49ers to pay starter's money to a backup.
Where he would fit with the 2011 49ers: McDonald would continue to be a key cog in San Francisco's defensive line rotation while seeing significant time on passing downs as one of San Francisco's top interior pass rushers. His role could increase if the 49ers lose Aubrayo Franklin in free agency and decide to move starting left end Isaac Sopoaga inside to nose tackle.
How he would be replaced: The 49ers would have to find another player to fill McDonald's shoes in the defensive line rotation. Veteran reserves Demetric Evans and Ricky Jean Francois would be the top in-house candidates, but neither have performed at the same level as McDonald. Will Tukuafu, who spent most of his rookie season last year on the practice squad before joining the 53-man roster in December, is a young player the 49ers would like to develop at the position and could step into McDonald's role.
Market level interest: Receptive. McDonald is sure to get some looks on the open market if he becomes an unrestricted free agent. He has value and upside as a pass rusher and rotational defensive lineman.
49ers interest level: Elevated. The 49ers realize McDonald's value and importance to their defensive scheme and want to keep him. San Francisco will compete to keep McDonald should he hit the open market.