As I recall, LLeyton Hewitt wears full length 'computer' socks on court.

If this is the case then he should be aware that the continual presure applied to the calf muscle from these socks is enough to slightly restrict blood supply. Over years of competition and in particular over a lengthy match on court, this reduced blood flow can cause weakness in some areas of the calf muscle leading to spasm and muscle tearing.

This is also a common injury in indoor cricket where it first came to my attention. The solution is to cut the tops off the computer socks or if you are Hewitt, get a specially designed sock that does not hug the leg.