Louis van Gaal has confirmed David de Gea could make his first appearance of the season against Liverpool - but has challenged him to prove himself in training first.

De Gea signed a new Manchester United contract on Friday to bring the protracted saga surrounding his failed move to Real Madrid to a close.

While his manager believes he is mentally ready to be thrown straight into the starting line-up for Saturday's encounter, he has warned that he must demonstrate his quality and concentration in training.

"It's logical that his head is empty now. He can concentrate and focus on the match. It's a big change," Van Gaal told reporters.

"I hope I can see that, also in the training sessions, so I can give him his first line-up position. But you have to show it, on the training session and matches, it's the same for Sam Johnstone and Sergio Romero.

Saturday's clash at Old Trafford could also see Anthony Martial make his United debut but Van Gaal has pointed to Angel Di Maria and Radamel Falcao's failed spells at the club as reasons not to put undue pressure on the France starlet.

"You hear people saying '50 million? He has to score!' No, he's 19, he has to adapt," said Van Gaal.

"It's very difficult. You can see how Di Maria has struggled, he was 27, Falcao was 29.

"At United, the pressure is much higher than at other clubs. We don't have to give him too much pressure, but of course, he has to adapt to our culture, our philosophy, and that's difficult enough. Maybe he can show some of that this season."