Scharner spent over five years with Latics before leaving for West Brom in the summer of 2010 but Robert Martinez has moved quickly to draft him back in after being hit by an injury crisis.
The Austrian has been brought in to play at centre-back to cover for the injured Ivan Ramis but he can also be pushed into midfield if needed between now and the end of the season.
"He knows the football club, we know him well, he has incredible experience and is a meticulous professional which means he is always in a great physical condition," Martinez revealed.
"He is desperate to come in and help the team and fight for his position. For us, it couldn't be a better option."