The defending NBA Champions San Antonio Spurs are off to a frustrating start.

With a 21-5 record, the Spurs are in fourth place in the Southwest division behind the Memphis Grizzlies, Dallas Mavericks and Houston Rockets. The team is also in seventh place in the Western Conference.

With so many injuries to key players and fatigue from the veterans kicking in, the Spurs have to consider searching for free agents. Here are five free agents the Spurs may want to keep an eye on.

1. Ray Allen

As we all know, Ray Allen is the big name who is still unsigned. The problem is that he is undecided about his future. When the season began, Allen had a lot of interest in the Cleveland Cavaliers because of the additions of LeBron James and Kevin Love. But with the Cavaliers struggling, Allen has been contemplating retirement. The Golden State Warriors have also been in the Ray Allen mix. Allen is the greatest perimeter shooter in NBA history, regular season and postseason, and the Spurs should make him an offer. Allen and Danny Green each taking three point shots together would be something special to watch.

2. Jermaine O'Neal

Another player from the 1996 NBA Draft. The Spurs have a quality defense, but when you play in the Western Conference, the grind never stops. Adding this 6-foot-11 big man would help the Spurs bench and help limit Tiago Splitter's minutes. Last season O'Neal averaged 7.9 points per game despite playing just 20 minutes per game, and he made 75 percent of his free throws. The Portland Trailblazers and Mavericks have been interested in O'Neal, so time may be limited for the Spurs if they want this free agent.

3. Rashard Lewis

If you can't get Allen, Rashard Lewis would be the next best three point shooter to add from free agency. Since entering the NBA in 1998, Lewis has led the NBA in three point shooting in 2008, won an NBA Finals and he provides a lot of experience. Lewis does have some injury history that can't be overlooked, however. You won't get the same Lewis who once lit up scoreboards with the Orlando Magic, but you do get a productive bench player that stands 6-foot-10 and can hit outside shots.

4. Al Harrington

Kawhi Leonard's is expected to return to the Spurs in two weeks. His injury has been described as one of the weirdest ever. Al Harrington isn't as good as Leonard, but he provide some relief for the Spurs in the mid range game, offensively and defensively. Harrington averaged 5.6 rebounds per 36 minutes last season with the Washington Wizards, and 8.2 the year before with the Magic. The Spurs division rival Rockets have shown attention in the 34-year-old power forward.

5. Emeka Okafor

This would be a risky decision, because Emeka Okafor has been fighting a lot of injuries lately. Although a very skilled player, Okafor missed all of last season because of a herniated disk in his neck. The Cavaliers are among the top teams who have shown interest in the 32-year-old big man. Okafor brings an all around game with rebounding, scoring and average free throw shooting. Maybe there's a chance the Spurs can convince Okafor to play, knowing he would have a chance to win his first career NBA Championship.

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