The winger has not recovered from a calf injury he picked up before the victory over Everton and joins Luke Shaw and Paddy McNair on the sidelines
Manchester United will be without Ashley Young and James Wilson in Wednesday’s Champions League encounter with CSKA Moscow.
Young picked up a calf injury ahead of this weekend’s 3-0 win over Everton and has not recovered in time to make the squad for the trip to Russia.
Wilson, meanwhile, is suffering from an illness and will not travel, while long-term absentees Luke Shaw and Paddy McNair are also unavailable.
“It’s the same amount of injuries so Luke Shaw, Paddy McNair and Ashley Young are not going with us,” Van Gaal told MUTV.
“Willo was a little bit ill – Wilson as he is named but, for us, it is Willo – so he shall not travel with us.
“I’ll take 20 players with me. It’s a four-hour flight so, if a player gets ill, I have the other player in my environment.”
Meanwhile, Sergio Romero and Antonio Valencia return to the squad after they were rested against Everton following their World Cup qualifying exertions in South America.
“Of course that was the reason Romero and Valencia were absent,” Van Gaal said.
“They have to cope with the jet-lag so I didn’t think it was wise to take them with us against Everton.”
United have collected three points from their opening two Group B fixtures, beating Wolfsburg 2-1 after losing by the same scoreline against PSV.