Playing alongside a host of first team players who were looking to work on their fitness, Keane shone in attack, opening the scoring after just 13 minutes and later scoring a second half hat-trick, including this impressive lobbed effort.
Keane had only managed one goal in 20 Championship appearances during his loan spell. He only has four senior league goals in his career, but showed in this display what he is capable of.
Van Gaal has come under criticism for allowing so many of United's forwards to leave without finding adequate replacements, with Javier Hernandez scoring freely for Bayer Leverkusen and 20-year-old James Wilson catching the eye at Brighton.
Keane attributed his five-goal haul to the "luck" his girlfriend brought him by "wearing this hat".
Think my girl brought me luck tonight wearing this hat! #5 @thatbrunettegirlmeg @rioferdy5 @5magazine
A photo posted by Will Keane (@wkeane48) on Feb 8, 2016 at 3:29pm PST
He will be hoping that his goals will allow him the opportunity to play in the senior team with attacking options thin at Old Trafford.
Keane has only previously played four Premier League minutes in one substitute appearance for United back in 2011/12.
Not a bad nights work! Felt amazing to back playing at OT.. Helps when you bag 5! #Mufc #5 #theatreofdreams
A photo posted by Will Keane (@wkeane48) on Feb 8, 2016 at 2:25pm PST
There was bad news for Van Gaal, however, as Adnan Januzaj, having returned from a loan spell at Borussia Dortmund, limped off with a hamstring injury after just half an hour.
Memphis Depay also stood out for United, setting up two of Keane's goals as he looked to get some game time under his belt having found his first team chances few and far between in recent months.
Phil Jones played the best part of an hour as he stepped up his recovery from the ankle injury he suffered against Swansea last month.
Andreas Pereira scored United's fourth goal from the penalty spot while Sergio Romero kept a clean sheet.
- Telegraph