He cannot wear the ihraam garments – can he enter ihraam in his own clothes?

Yes, if a person is unable to wear the ihraam garments, then he may wear whatever is suitable of other, permissible clothing. According to the scholars he has to slaughter a sheep and distribute its meat to the poor, or feed six poor persons, giving each one half a saa’ of food, or fast for three days.

This is what the scholars said, by analogy with what was narrated about shaving the head, as Allaah says (interpretation of the meaning):

“and do not shave your heads until the Hady reaches the place of sacrifice. And whosoever of you is ill or has an ailment in his scalp (necessitating shaving), he must pay a Fidyah (ransom) of either observing Sawm (fasts) (three days) or giving Sadaqah (charity — feeding six poor persons) or offering sacrifice (one sheep)”

[al-Baqarah 2:196]

And the Prophet (peace and blessings of Allaah be upon him) explained that fasting means fasting for three days, giving Sadaqah (charity) means feeding six poor persons, giving each one half a saa’, and that sacrificing means slaughtering one sheep. The sacrifice and feeding of the poor in this case should be done in Makkah, in order to be on the safe side, because his breaking the rule concerning clothing will last until he exits ihraam.