He doesn't call it a slump; rather, a funk. Still, after hitting .252 in the first two months of the season, Duncan was optioned to Triple-A Memphis on May 29 and the Cardinals called up Joe Mather.
"It is humbling," Duncan said, "but at the same time, it's a part of the game. You have to continually play well to stay there. It's just baseball."
Now he has a chance to redeem himself -- to pull himself back up.
Although the organization cannot be happy with Pujols going on the DL, it is an opportunity for Duncan to reach deep down and make a case for why he deserves to play at the Major League level.
The swing that produced 42 home runs in 174 games over a two-year period has vanished. When the Cardinals faced a stretch of five left-handed pitchers over seven games to open June, the organization felt Memphis was a better place for Duncan to rediscover his power stroke.
It doesn't help, for Duncan, that the Cardinals have anything but a lack of talent in the outfield. Ryan Ludwick, Rick Ankiel and Skip Schumaker have all produced with Brian Barton as a capable reserve. Mather pounded the baseball in Triple-A and a talented Colby Rasmus waits in Memphis until his numbers improve.
So it made sense to the front office to send down Duncan, even though he did not necessarily agree with the decision. Now, after playing in only six games before rejoining the Cardinals, Duncan believes the change of scenery -- if he does return to Memphis -- will do him good.
"It kind of allows you to play in a less-pressure environment," Duncan said. "Get yourself back into a groove."
When Duncan was sent down, general manager John Mozeliak said it was temporary and said the length of his demotion would depend on how the next few days and weeks played out.
When Pujols crumbled to the ground in pain, Mozeliak had to alter his plans for Duncan dramatically.
"I don't think he struggled down here," Memphis Redbirds manager Chris Maloney said. "He's hit a couple of balls on the nose, right at people."
While it is hard to make an assessment of a player after only six games, Duncan did not work into a groove. He only had four hits in 21 at-bats, though he smacked a double off Iowa Cubs starter Sean Marshall on Monday.
So what went wrong over the past 10 months? Duncan doesn't quite yet know, but he is adamant that the hernia had nothing to do with it.
Though he did not commit to season-ending surgery until Sept. 15 last year, Duncan began to suffer a significant drop in his numbers toward the end of July. In every category, the once-dominant outfielder suffered offensively.
"I definitely think it slowed him down," Mozeliak said. "Obviously, before that he was putting up some very good numbers. More importantly, I think he feels good about himself and getting the opportunity to play."
Over the final 1 1/2 months, Duncan hit .165 with one home run and 11 RBIs in 103 at-bats in 43 games. This year has not gone much better. Though the average is up, he only hit four home runs and drove in 16 runs for the Cardinals.
The 22 home runs he hit in only 280 at-bats in 2006 may seem like a long time ago to Cardinals fans, but not to Duncan. That year, he ranked third in the Majors for number of plate appearances between home runs.
This year, seeing Duncan hit a home run has been anything but common.
"People try to make it seem like I wasn't doing well at all," Duncan said. "I'm not playing at the same level I played at the last two years. But I'm still digging in, competing and taking quality at-bats."
Staying positive throughout the toughest part of a young career could destroy the will of some athletes. But Duncan understands the process and he has been around baseball his whole life -- his father Dave is the Cardinals' pitching coach and has played or coached the game for the past 45 years.
Playing in Memphis, he said, was an opportunity to find himself again.
"The one thing he's dealing with is adversity," Mozeliak said. "He's one young man who's done that throughout his career and he's been successful. I think that's something he'll get back soon."