Ifill, an English-born Barbados international, took to Twitter following the game against Adelaide United to voice his frustrations over the incident, and the Phoenix yesterday confirmed it had formally approached Football Federation Australia to ensure the matter was fully probed.
A spectator at Hindmarsh Stadium was heard to call Ifill a derogatory racial term after he was substituted in the 61st minute of the 3-1 loss, AAP reported.
Wellington Phoenix general manager David Dome yesterday would not comment on the nature of the abuse but said the club was treating the allegations very seriously.
''Our guys reported it to the match commissioner, who took it up with Adelaide United, and Adelaide's taken it up with the police over there,'' he said.
''As the investigation unfolds I'm sure it will all come out and it will be resolved. We're confident the processes are correct and the right things are in place.''
Dome said the Phoenix had no opinion over what punishment should be meted out if the allegations are proven true, preferring instead to leave it in the hands of the FFA and the South Australian police.
It is thought to be the first incidence of a player being racially abused by a supporter during an A-League game. FFA chief David Gallop said yesterday the spectator, if found, would be banned from attending games.
''That kind of taunt is not on,'' Gallop said.
Gallop believed bans were appropriate sanctions for racist supporters, rather than seeking to make racist abuse a criminal offence.
''We have seen overseas there can be criminal sanctions with that kind of thing,'' Gallop said.
''The ban system that is in place for any kind of antisocial behaviour is one we need to continue to be vigilant about.
''At this stage, the ban system is the way to deal with these things.''
In a statement, Adelaide United said the club was assisting the FFA in its investigation and it conveyed its concerns to Ifill. The Phoenix said it had accepted an ''unequivocal apology'' from Adelaide.
Following the match, Phoenix coach Ricki Herbert said it was not his place to confirm the nature of the allegations.
''There was a few comments that we have shared with the club officials ... with regards to a player.''
Ifill, the Phoenix's all time leading scorer, could not be reached for comment yesterday but he was less cagey on Twitter, saying he had received racist abuse from a ''very small minority'' of fans.
Responding to a question from former Phoenix and current Sydney FC chief executive Tony Pignata, Ifill tweeted: ''not happy been a long time since [I've] had to deal with anything like that''.
He later wrote it was an isolated incident and the first time it had happened to him in the A-League, confirming his complaint pertained to ''a few things that were blatantly racist that I'd rather not repeat''.
