Ervine, who arrived in Perth last week after damaging his knee in Hampshire's last match of the season, will be examined by WACA doctor Damien McCann next week.
Early reports claim the 22-year-old suffered significant structural damage to the knee, which he first injured while playing for Zimbabwe three years ago.
He could be out of action for the entire southern hemisphere summer but hopes to be fit to play for Hampshire next year as he attempts to qualify for England.
"It is very disappointing but we will not have the full picture until next week," WA coach Wayne Clark told the West Australian newspaper.
"It looks as though he will require surgery of some sort but we don't yet know how bad it is or what he has got."
Hampshire will cover the cost of any surgery and rehabilitation but the injury has still come as a blow to the Warriors who had pencilled in Ervine for a One-day berth this season.
Ervine helped Hampshire to a One-day title this year with centuries in the semi-final and final of the C&G competition and had been closely monitored by the WA selectors as a replacement for retired Kade Harvey.
WA chairman of selectors Tom Hogan said recently that the former international, who scored a century for Zimbabwe in Adelaide two years ago, was making a strong claim for inclusion.
"We're excited that he is doing well," Hogan said. "Sean is a good option for us if he is starting to take wickets and score runs."
Ervine could not force his way into the WA team last season in the first year of his contract, producing only modest club form for Fremantle.
He is playing for Hampshire on an Irish passport and will become available for either Australia or England after completing a four-year residential qualification. But he favours playing for England.
"Hampshire have given me an opportunity and it's been amazing how I've just sort of fitted in and just enjoyed all the cricket, so at the moment it's sort of leaning England's way," he said.
Australia opening batsman and WA captain Justin Langer has also been impressed with Ervine's development and said he had been fast-tracked by playing with Shane Warne at Hampshire.
"He is a really good kid," Langer said before Ervine hurt the knee. "Given his extra six months experience, playing with Warney and a few senior players at Hampshire, he is coming along really well."
Ervine's hopes of playing regularly for WA as an overseas player are also in doubt as Sussex all-rounder Murray Goodwin has relinquished his Australian citizenship to play in the county circuit as a local.
He is now classed in the Pura Cup as an overseas player, and only one of the pair can play for WA at a time. In the 2003-2004 season Goodwin broke Simon Katich's record (1,145) for most runs by a WA batsman in a Pura Cup season with 1183 runs in 10 matches.
Goodwin played Test and One-day international cricket for Zimbabwe before choosing to retire and play for the Warriors.