Louis van Gaal claims Manchester United's defensive solidity has prevented Sergio Romero from demonstrating if he can become David de Gea's regular replacement in goal.

Romero has only conceded once in four outings for United so far, an unfortunate Michael Carrick deflection beating him in a 3-1 UEFA Champions League play-off win over Club Brugge.

That form will have reassured many United fans, with De Gea expected to leave Old Trafford for Real Madrid before Tuesday's transfer deadline.

However, when asked if Romero had proven he could handle the physical challenge of Premier League football, something De Gea himself initially struggled with after joining from Atletico Madrid, Van Gaal was non-committal.

"I don't think so because, until now, we don't allow a lot of shots or moments in our area," Van Gaal said. 

"He has made very good saves, but until now, I think only maybe the save against Brugge at 1-0 was very important and he did also a save against Tottenham Hotspur and that was it. 

"He has not been able to show what he can do, and I think that is a compliment to the team."

Romero's strong start to life at Old Trafford has not surprised the Dutchman, who previously won the Eredivisie with the Argentina keeper as his first choice at AZ.

Van Gaal added: "We have had special training sessions with him, not just him and the goalkeeping coach, but with him and the players. 

"We have given a lot of attention to that and this is why we could overcome it. 

"I am not surprised that we are doing well with him because, as you know, the defence starts with the striker. We have proved that already last season that we have a very good defensive organisation.

"It is not unexpected for me, we have bought him. Otherwise we wouldn't have bought him. 

"You have expectations always when you buy players. Mostly you have positive expectations."