The R'n'B star got her big break after auditioning for the Def Jam Records boss, but now he is said to be concerned that she is overdoing it.
A source told Look magazine, 'Rihanna's professional, works hard, and stays away from drugs and alcohol, but Jay wants her to be careful.
'He told her to take a holiday for a week - she's been working flat out and needs to get over the bronchitis, which he's sure she's developed as a result of stress.
'He told her she'll be alright, but to keep her head down.'