Wilson came into this season as the eighth-inning setup man. League, who came into last season as the closer, came into this season without a defined role.
Mattingly concedes he's "concerned with Wilson's success," convinced, he said, that the right-hander's twice-repaired elbow is sound.
"But compared to last year, he's been a lot more stressful," Mattingly said of Wilson's outings. "Last year, it was clean, clean, clean. This year, it hasn't been the same. Yet. I really believe he'll get there. At this point, he's not."
So, does that mean League has earned a promotion to the back end of the game?
"Slowly, but surely, it's changing," Mattingly said of League's role. "The more you send a guy out there and the more outs he gets, you gain confidence in him."
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.