Scotland are currently at the foot of the 2014 World Cup qualifying Group A with two points from four matches.
"Scotland have to come third in the current group," Nevin told BBC 5Live.
"If he gets us to third place, the position in the next group of pots when the draw is made for the Euros is much better. Thank goodness he is in - he has to make a difference.
"It's a tough job and you need a big personality to come in and do that job. He's proven, he's Scottish and he's accepted by the Tartan Army, but he has a massive job to do and it starts right away."
Strachan has managed Celtic and Middlesbrough among other clubs in his career.