Shelvey has been a hugely-influential player for Benitez in the Championship this season.
The midfielder – who has a Football Association hearing into a misconduct charge next week – was superb in Saturday's 4-0 win over Birmingham City.
"I think he knows he has our confidence," said United manager Benitez, whose side face Wigan Athletic at the DW Stadium tomorrow night.
"He's trying to play his best football. He's someone that's keen to pass the ball and be involved in the game. He has the freedom to do it. With (Isaac) Hayden around, it has good balance.
"He knows what he has to do."
Shelvey has denied a FA charge of using racially-aggravated language towards a Wolverhampton Wanderers player in September.
The 24-year-old will go before an independent commission early next week.
"For him, it's important to concentrate on the pitch," said Benitez. "He's a good player. If he can stay focused on football, he will do well and be another key player for us."
Shelvey, signed from Swansea City in January for Â£12million, is second in the Championship assists table, having set up six goals so far this season.
The England international had the red card he was shown in last week's 2-1 defeat to Nottingham Forest overturned on appeal.