The Dutch boss, who took over after leading the Netherlands to third place at the World Cup last month, was left with plenty to ponder ahead of Saturday's Premier League opener against Swansea.
Wayne Rooney, captain for the night, missed a penalty but Darren Fletcher drove in United's opener shortly after the interval only for Rodrigo to equalise in the 71st minute before Fellaini scored his first goal in United colours.
He also endeared himself to the United fans by greeting lots of them at the front of the South Stand as he made his way to the dug-out after half-time.
With Robin van Persie, Danny Welbeck, Jonny Evans, Antonio Valencia, Nani, Anderson and Wilfried Zaha, as well as the injured Michael Carrick, among those watching from the stands, Van Gaal selected a makeshift side.
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Although under less pressure, the defence retained the ball far better than in their recent 3-1 friendly win over Liverpool.
Ander Herrera, making his first home appearance since joining from Athletic Bilbao, impressed with his willingness to dictate play sitting in front of the back four.
But Van Gaal will want to see much more from his new team when the competitive action starts on Saturday. Nuno Santo's Valencia do not begin their La Liga campaign until they face Sevilla on August 23 but they started with the greater impetus, midfielder Sofiane Feghouli driving over from distance in the early stages.