Final answer:
A patient with a 'foot slap' at heel strike is likely suffering from ankle dorsiflexor weakness, which causes the foot to drop uncontrolled onto the ground due to inability of the muscles to slow down the foot's descent.
Step-by-step explanation:
The patient exhibiting a "foot slap" or difficulty supporting weight at heel strike is most likely struggling with ankle dorsiflexor weakness. When the dorsiflexors, which include muscles such as the tibialis anterior, are weak, they cannot effectively slow down the foot's descent following heel strike during the gait cycle. This can lead to the characteristic 'foot slap' as the forefoot drops onto the ground uncontrolled. In contrast, weakness in other muscle groups such as the triceps surae (calf muscles), would lead to different walking abnormalities, such as difficulty with pushing off during toe-off or maintaining posture during the stance phase of walking.