The 51-year-old former Wycombe, Northern Ireland and Fulham boss will assist caretaker manager Giuliano Grazioli in the Bees' last four matches of the season.
Barnet are second-bottom and lie three points from safety but Sanchez said: "I've come in to help Giuliano, who is a football acquaintance, with the big task of helping Barnet off the bottom rungs of League Two."
Grazioli added: "This is an opportunity for me to learn from someone with experience at Premiership and international level. He has so much to give and there is a lot I can learn.
"We've got a job to do and three weeks to get it done."
Ex-Barnet striker Grazioli was placed in charge last week following Martin Allen's shock departure to Notts County.
Source: PA
