Cahill will be lost to Everton this month due to Australia's Asian Cup campaign.
Moyes is now weighing up whether to switch wideman Pienaar into a supporting role when Cahill leaves.
Moyes said: "I'm considering pushing Steven forward with more involvement, where we might create more chances.
"I don't know whether he'd get us more goals but he has great ability and is capable of doing it - as he has done so for South Africa. I wouldn't play him up front but off a frontman.
"Tim's attributes are hard to bring from elsewhere but someone offering something different may alter how we play."