Faletau had a scan on an injured ankle last night which revealed ligament damage ruling him out of action for up to six weeks.
“Toby has ligament damage to his ankle and will be in a boot for a period of two to three weeks,” said Wales physiotherapist Mark Davies.
“He will then begin rehab meaning he is ruled out for around six weeks.”
McCusker has three caps, appearing as a substitute against South Africa at the Millennium Stadium last summer before entering proceedings from the bench for both Tests of the following tour of New Zealand.
