The Argentina winger, signed for a British transfer fee record £59.7 million from Real Madrid, will miss his third consecutive game after failing to recover from a hamstring injury.
The 20-times English champions will also have to cope without injured defenders Luke Shaw andChris Smalling as well as midfielder Daley Blind.
But United manager Van Gaal remained upbeat on Friday, saying he can see an end in sight to the injury crisis that has plagued his reign at Old Trafford and, at times, has seen him have 12 players unavailable at one time.
“Now I have only four players injured, so that’s better than ever I believe,” the Dutchman told reporters.
Rafael and Phil Jones are both back from their long-term groin and shin injuries.
United are third in the table with 28 points from 15 games, eight behind leaders Chelsea, and have won their last five matches. Liverpool have endured a stuttering start to the season and are ninth, seven points adrift of Van Gaal’s side.
The former Netherlands coach will experience the ferocious rivalry between the two sides for the first time on Sunday, but has sought advice from long-serving members of the club to fully understand a fixture that is always intense and often fractious.
“I have an assistant manager in Ryan Giggs, and he presented an analysis of Liverpool and he did it in a marvellous way, so I’m very pleased,” Van Gaal said of United’s record appearance maker.
“We (also) have a cook and his name is Mike and when I don’t know about anything to do with United and rival clubs he shall say it. He is a big Manchester United fan and I hear immediately from him.”
After suffering home defeat by Swansea City in his first game in charge, Van Gaal’s side have won six and drawn once in eight games at home.
“(It was) unbelievably disappointing to lose the first match at home as you have to make a fortress out of your home stadium,” he said.
“Now we have shown that and we hope to continue that against Liverpool.”