The Belgian winger was deployed in a more central position during United's 3-1 International Champions Cup win over Barcelona in California on Saturday, scoring the sealer in injury-time after Wayne Rooney and Jesse Lingard had given them a two-goal lead.
Of Januzaj's performance, van Gaal said: "I have given him a chance in this position and you have to look if he can do that or not. But he has a lot of quality and against Barcelona he showed it for the first time.
"He was very good and was a threat as a striker in his 30 minutes. He always gives an option for midfielder and defenders, he scored a wonderful goal and that is always important."