But the experienced shooter is hopeful the Vixens can break a four-game losing streak when they play the Southern Steel in Dunedin tomorrow night.
The defending champions have not won since their round five victory against the Northern Mystics and desperately need to win to keep their play-off prospects alive.
"If we knew exactly what was going wrong we'd fix it straight away," McMahon said.
"The last four weeks that we've played haven't been great . . . but we had a great start to the season and, I guess, that is what gives us hope."
The Vixens picked up where they left off in 2009, winning their opening five matches. But they were knocked off their pedestal when the Queensland Firebirds thumped them 62-41 in Brisbane last month and have looked far from formidable since.
A knee injury to Australian defender Julie Corletto has not helped and, perhaps, it is no fluke the form slump coincided with the absence of key playmaker Natasha Chokljat.
The centre aggravated a calf injury in the 62-51 win against the Mystics but is expected to return to court tomorrow night.
"It looks like it. She played half a match in our state league back here last week and has been completing the full training load for the last couple of weeks now. But she has been off the court now for five or six weeks so I'm sure it is going to take her some time to get back into it."
The Vixens, Steel and Mystics are all on 10 competition points and vying for a spot in the play-offs. The Mystics play the unbeaten New South Wales Swifts in Auckland this afternoon. If that match goes to form, the Swifts should extend their competition lead.
That means the winner of the Vixens-Steel match will be able to consolidate its place in the top four.
"Absolutely every match from now on in is a must-win, starting with this game... We're on the same points [with the Steel] and it is only goal percentage which separates us, so it is going to be a huge match for us."
