Jennings had experienced two dropped balls in the outfield over the past couple of weeks prior to Tuesday night's game, and Napoli's ball was a play that he normally makes.
A dejected Jennings, who is a Gold Glove-type center fielder, told reporters after the game: "I don't know what it is actually. It's a bad time to be playing bad."
Maddon said he had a "nice conversation with Desmond, who is pretty much in the listening mode all the time" and "listens well," noting that he just brought a couple of things to Jennings' attention.
"One, that he's really, really good," Maddon said. "Number two, that he's going to be a great player in this league. And don't ever worry about making mistakes here, don't ever. I'm never worried about anybody making a mistake here."
Maddon stressed to Jennings that he could "impact this game here for us, possibly like nobody else in our locker room can" based on his abilities.
"Just a reaffirmation of what you're all about and understand that we all get our confidence dinged once in a while, we all do," Maddon said. "Sometimes you just need somebody to remind you of what you're good at and how you absolutely are. So hopefully that will help a little bit, because I do believe in him a lot."
Bill Chastain is a reporter for MLB.com. Sam Strong is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.