As the days dwindle down before the start of the regular season, there are still many unanswered questions in free agency.

Now more than ever, the idea of having depth on the roster is crucial, and the San Francisco 49ers are surely lacking it in one of the most important positions on the field: quarterback.

With less than 50 days till the opening kickoff, the 49ers need to be on the hunt for a possible backup for the improving Alex Smith, but the NFC West Division Champions need to find someone with experience and leadership to back up their starter.

Smith easily had the best year of his career in 2011, throwing for 3,144 yards and 17 touchdowns, with only five interceptions. 

But if he were to get hurt this season, the 49ers offense would easily crumble.

Although Smith hasn't made the headlines in a while, Cris Carter on ESPN's NFL Live recently went on record to insist the team pursue recently retired quarterback Donovan McNabb.

McNabb, who turns 26 in November, became inactive following a brutal six-game span in Minnesota, but is reportedly in great shape having shed close to 20 pounds.

He has been training extensively over the summer with quarterback guru George Whitfield, who has him going back-to-the-basics through fundamental training on sand and in the ocean.

I've been in great shape. That was never the issue, McNabb said. I stay motivated no matter what.

Back in June, McNabb told ESPN that he is 80-90 percent positive that he will play this upcoming season.

He even mentioned that he was in talks with three different teams, though he neglected to disclose which ones.

I think teams are evaluating what they have. They are looking at their young quarterbacks, their backup situation. Obviously their starters they feel very confident in, but if things were to go wrong in training camp or maybe the competition isn't where they need it to be, they would obviously pick up the phone and call, McNabb said. Being an older player, I am focusing on strengthening my body as well as my mind.

The 49ers splashed headlines this offseason by bringing in veteran wide out Randy Moss from retirement. If head coach Jim Harbaugh doesn't mind adding a former star in Moss, he might be inclined to bring in McNabb, as well.

Durability remains a concern with McNabb. During his time with the Washington Redskins and the Minnesota Vikings, McNabb clearly was not the same quarterback he was while with the Philadelphia Eagles.

The six-time Pro Bowl star started to show signs of decline following his departure from Philadelphia. After throwing a career-high 15 interceptions, he was eventually benched in Washington, and was replaced by Rex Grossman, which many considered a bold move by Redskins head coach Mike Shanahan, who did not receive the production he expected from McNabb.

Washington would eventually release McNabb, and he eventually ended up with Minnesota, where his woes continued. After only six starts, he was bench for then-rookie quarterback Christian Ponder, simply due to lack of production.

In six games, McNabb threw for just 1,026 yards and four touchdowns. By early December, McNabb was released by the Vikings, which lead to the announcement of his retirement.

Many have blamed the systems he was in, and others have said that he wasn't given the proper tools to succeed. Aside from those possibilities, McNabb clearly was not the performer he once was.

McNabb is now out to prove his critics wrong.  He wants another shot to prove his worth, and formally end his career with a bang.

 Even these last two years, when people may look at it and say, 'Oh, he's done, or whatever.' I'm 34, 35 years old, but still, I played at the pinnacle, I played at the highest level of my career. I played there, McNabb told Fox Sports. And I would vote for myself for the Hall of Fame.

The 49ers are clearly lacking experience on the quarterback depth chart, with second-year backup Colin Kaepernick as their current best option.

McNabb can be very useful with the 49ers as smart player who can not only give his team a better chance on the field, but can be a mentor for the younger players on the team.

In McNabb's 13 seasons, he has passed for 37,276 yards and 234 touchdowns, and led the Philadelphia Eagles to four NFC Championship Game appearances.

You have to have short-term memory. You have some ups and down, you hit a wall. But it's the adversity, McNabb said. How you overcome that adversity. And for me, I see a positive light.

The 49ers are set to begin training camp in Santa Clara, Calif. on July 28.