The singer, who is currently starring in the off-Broadway production of The Fantasticks, revealed via Twitter on Monday that he's been sidelined with strep throat and will need to miss a few performances.
But Aaron added that his illness may be directly linked to the grief he continues to feel over his sibling's passing.
"Still missing my sister and now getting over the shock of her death," he tweeted. "It might have made me sick at this point. #RIP #LeslieCarter."
Earlier this month, Aaron took a brief leave of absence from the show to mourn the loss of Leslie, who was only 25 years old when she died at the end of January. While official autopsy results have yet to be released pending the toxicology tests, a police report obtained by E! News at the time suggested a possible drug overdose.
"Life is precious & fragile u don't realize it until u go through an experience like I have recently with my sister," Aaron tweeted yesterday. "Choose life. Not drugs.."
He also wrote that he's doing his best to recover, telling fans: "Miss you guys!!"