Hazrat Mahdi’s (as) cheeks will be sunken rather than full

The Messenger of Allah (saas) decreed; “… His cheeks seem to be less full and [when he is sleepless] he sometimes looks pale. …”

(Remembrance of the Beloved, Questions and Answers About Imam Mahdi (p.b.u.h), by Seyed Husain Husaini)