"It looks like he's (Fenton) torn a ligament in his ankle.  So it looks like we've lost two fullbacks.
"It's really disappointing to lose Tom Doyle because just about every game he plays he gets a yellow card and it's usually needless. So Tom Doyle's putting us under pressure now for the fullback role."
The niggly game featured nine yellow cards and Merrick twice criticised Doyle during the post-match press conference.
"Tom Doyle was unavailable last week and then he comes back and gets a yellow card.  I'm labouring the fact but it was very disappointing."
Merrick is hoping to get through coming weeks with other defensive options.
"I've got my fingers crossed for Ben (Sigmund) and Justin Gully," said Merrick. Both have been recovering from hamstring injuries.
"Young Dylan Fox had to have an injection in his ankle and we're hoping he might come up because we're pretty light on in the back line and have been for two or three weeks now."
The Phoenix remain sixth on the A-League points table.