Tim Duncan's subtle decline could be a huge problem for the Spurs

The Spurs have had a big problem ever since Tim Duncan stopped being the best player in the league: suddenly he needed to be surrounded by other big men that could handle things he wasn't capable of doing anymore. Matt Bonner, Antonio McDyess and DeJuan Blair all tried to fill that role to varying degrees of success but the two players that proved up for the task were Tiago Splitter and Boris Diaw.

Diaw allowed Duncan to play inside by stretching the floor just enough with his shooting while also providing smart defense and playmaking that Bonner couldn't offer while Splitter handled the toughest defensive assignment and protected the rim when Duncan couldn't, something Blair was not physically able to do. That three-man rotation plus spot minutes from Kawhi Leonard at power forward gave the Spurs their latest championship.

Unfortunately, Duncan has suffered a small, subtle decline from last season that could make even those combinations ineffective unless he bounces back and his two running mates return to the superlative level they showed last season.

Duncan's absent mid-range jumper makes him a full-time center

Big Fun remains a terrific rim protector, allowing just 46.9 percent on field goals he defends at the rim. That's better than Anthony Davis and Marc Gasol, for comparison. What has eroded badly is Duncan's performance on the offensive end. As Chris Itz so eloquently noted, Duncan has abandoned his jumper. In 2012/13, 31 percent of Duncan's points came from the mid-range. In 2013/14, that number had descended to 23.2 percent. This season it's at 18.4 percent. At one point Duncan had the offensive game of a power forward and the defensive game of a center but now he is strictly a five on both ends.

Obviously, that has made finding lineups featuring Duncan and Splitter that work a tall task. With the Duncan-Splitter tandem on the floor, the Spurs have scored only 98.5 points per 100 possessions, which is a lower offensive rating than the worst offense in the league has. The spacing is so obviously cramped that numbers seems superfluous but Splitter is finishing 2.5 percent fewer plays as the pick and roll dive man this season and his field goal percentage goes up by a full four percentage points when he doesn't share the court with Duncan. Splitter's declining numbers are not solely related to poor spacing -- he hasn't look all the way back from his injury yet -- but it's definitely not helping him regain his rhythm.

Duncan is not an elite inside scorer anymore

If the spacing with Splitter and Duncan on the court together was their only problem, the Spurs could survive and even thrive by separating them and having Diaw play the majority of the game next to Tim, providing him with enough room to work on scoring inside. Only that doesn't work either because Diaw is struggling severely with his three-point shot yet the percentage of his total field goal attempts that have come from beyond the arc represents a career-high. While his inefficiency from outside is no one's fault but his, the fact that Diaw is taking so many threes goes back to Duncan clogging the lane. Diaw takes more threes with Duncan on the floor than off and is not hitting enough of them to make the pairing work. The Spurs are scoring only 102.3 points per 100 possessions instead of the 108.6 they put on the board last season and the two percentage points dip in three-point shooting has a lot to do with that.

Even if Diaw or Matt Bonner were actually hitting their threes, going four-out to create space for Duncan is not a winning formula anymore. Among players who have finished possessions with a post up at least 150 times, Duncan ranks 32nd of 34 players, ahead of only Andre Drummond and Dwight Howard in terms of points per possession, per Synergy Sports. Last season he ranked 12th among players who finished at least 250 possessions with post ups. Duncan barely turns it over in the post but also doesn't draws many fouls. Something very similar happens when he's the roll man on pick and roll, where he is better than last season but not still not great despite having cut down the amount of pick and pop jumper he takes.

Duncan eroding post game combined with his inability to hit mid-range jumper to work the pick and pop consistently really hurt the Spurs' lineup versatility. While Parker's struggles are getting the most attention because they are more easily recognizable, Duncan's subtle decline as a shooter and post threat is as big a problem for the Spurs right now.

Is it possible for him to bounce back?

The only way to begin to even diagnose how serious the situation the Spurs find themselves in really is would be for Splitter and Diaw to go back to being the players they were last season, as simplistic as that sounds. Because the only way of knowing if this version of Duncan is the only one that exists anymore is to provide him with the version of the players he had last season and see if the problems he's having on areas he excelled at then are a product of having to make up for his teammates' failings or signal a genuine decline.

To be fair to Duncan, there have been some signs of life lately. He has been hitting more of his jumpers than early in the year, going 6-for-14 (42.9 percent) in shots beyond 16 feet in the last five games. He also destroyed the DeMarcus Cousin-less Kings a few games back in the post. A few more good performances in a row would form a nice trend to build on for Duncan as he waits for the other members of the three-headed monster that was last season's big men rotation to round into form.

Even at 38 years of age, Duncan is one of the best players in the league. The small dip in production wouldn't even be noticeable if not for the fact that so many other things have gone wrong for the team this season. Yet as the playoffs near, it serves as another reminder that this isn't the same squad that won the championship last year yet and that it might never reach that level again. Duncan has faced tougher challenges and prevailed. Hopefully he has one more renaissance left in him.