The Scot says the teenager, who did not even make the matchday squad for the midweek clash with Manchester City, has played an "incredible" amount of games this season
The 19-year-old attacker made an electric introduction to his Old Trafford career, scoring twice on his first Premier League start at Sunderland in October and impressing many with his tricky wing play.
But Januzaj has featured just twice in March, missing out on the matchday squad altogether for last Tuesday's loss to Manchester City.
United host Aston Villa on Saturday before a crucial Champions League quarter-final first leg against Bayern Munich at Old Trafford, and Moyes insists the winger is still a big part of his plans.
"I think Adnan has played an incredible amount of games for a 19-year-old," the Scot told reporters.
"We have to be mindful of that. We have seen signs in training that we have to be careful what we do with him.
"He is a great talent and he is someone we know will go a long way at Manchester United. But we are just being careful with him.
"We have to do the right things and he has played a lot of football."