The 28-year-old Dutchman signed on a non-contract basis with the Boundary Park club last week and will stay with The Latics as they push for promotion to Division One next term.
The former Huddersfield and Preston marksman had trials at Barnsley and Turkish giants Galatasaray this summer before joining manager Iain Dowie's side.
At a press conference, Wijnhard told the Oldham official website of the car crash he suffered 18 months ago that nearly killed him when he was a Huddersfield player.
Wijnhard said: "I went out with a friend of mine, I had a drink so I let him drive back and he just fell asleep at the wheel, we spun on the road hit the barrier and rolled over eight times and hit a couple of trees."
Dowie added that he has been eyeing the Dutchman since last term and is delighted to have signed him for the rest of the season.
The Latics boss said: "He brings a little bit of experience and has immense power, I think he can be a real threat.
"He has a steely determination to win things."
