Shaw, 20, is still in hospital in Eindhoven after his leg was broken in two places by a flying tackle from PSV Eindhoven’s Hector Moreno in the early stages of their Champions League match.
Van Gaal, speaking to reporters before United play Shaw’s former club Southampton in the Premier League on Sunday, said: “I called him last evening and he sounds very strong.
“Amazing for me. Big surprise. A good signal.
“It is not easy but his family is there. We have sent people to him. Maybe he shall come back tomorrow but then there will be a long period of rehabilitation. There is still a long way to go.
“I am always looking at the whole human being, saying that it is not just physical but also mental.”
The immediate cost of the injury for United is the end of the developing left-wing partnership between the defensive Shaw and the more attacking Memphis Depay ahead of him.
Van Gaal continued: “For us it is a big loss, a big loss for the team because I said already that it shall be the season of Luke Shaw and now its finished.
“He started so well and we built up the left wing with Memphis Depay and we have to restart and build it up again because we have to fill that position. We will have to cope with it, but it is a big loss.
“It’s also difficult for the player who has to replace him. But we have in (Daley) Blind, ((Marcos) Rojo and in Ashley Young, good replacements.”
The game brings Van Gaal face to face with Saints manager Ronald Koeman — a compatriot, former friend and ex-Ajax Amsterdam and Barcelona colleague — and United will start as favourites to win.
They are third in the table after winning three of their opening five matches while Southampton are 11th after winning one, drawing three and losing one of their opening games.
Van Gaal was non-committal over whether he would have a drink with Koeman after the match, but was more forthcoming when he was asked about Wayne Rooney’s hamstring injury that kept him out of last week’s 3-1 win over Liverpool as well as the 2-1 defeat at Eindhoven.
“He is back, it was a minor injury and we didn’t want to take any risks, but he has had his treatment and his training sessions so I think he can start.”
(Reporting by Mike Collett, editing by Alan Baldwin)