Mata will return to Chelsea as a Man United player for the first time since his move in January 2014.
The Spaniard is in fantastic goalscoring form having registered memorable strikes against Manchester City and Liverpool in recent weeks.
Van Gaal revealed that Mata will play as he usually includes his players against their former clubs.
When asked about Mata playing against Chelsea, van Gaal said: ”Normally I always put players in the line-up if they’ve played for the opponent, so I think Mata shall play.”
Jose Mourinho was said to be happy to let Mata leave Chelsea as he wasn’t impressed with his defensive contribution. The 26-year-old will be hoping he can inflict some pain upon his former employers.
United will have every right to be confident of getting a positive result as they are coming off the back of a six-game winning streak in the Premier League. However, Mourinho has an excellent record at Stamford Bridge and will be boosted by injuries to United’s Michael Carrick, Marcos Rojo, Phil Jones and Daley Blind.