The 69-year-old, who has already brought Ashley Young, Phil Jones and David de Gea to Old Trafford, conceded that they are unlikely to be joined by any more new faces.
"We lost five players in their 30s this summer,” he said. "That helped finance the three younger players - Ashley Young, Phil Jones and David de Gea - I have brought to the club.
"At this moment, I can't see another addition. The type of player we might have been looking for is not available.
"I am happy with the players I have got at this moment in time."
United are currently on a pre-season tour in America and take on an MLS all-star team at the Red Bull Arena on Wednesday.