Speaking to ESPN FC's Rob Dawson, Neville said the dressing room would have been "shot to pieces" if the team witnessed an exodus from Old Trafford.
"I think there are three or four players at Old Trafford who have higher levels of quality that in a perfect world, Ole would probably like them all out at once.
"But actually, if they left it would weaken the team that badly it'd mean that they wouldn't challenge for the Champions League. I think what Ole has to do is to get rid of one at a time. I think it's a clever transition out of what has been a poor transfer strategy for the last four or five years.
"You can't get out of it in one year, it's going to take two or three years of good culture and tone, in terms of what they're doing, to get out of what they've done. You can't lose Lukaku, [Paul] Pogba, [Anthony] Martial all in one -- you'd be absolutely decimated.
"The dressing room would be shot to pieces. You could maybe lose them over a period of two or three years if they wanted to leave."
The Red Devils begin their Premier League season on Sunday against Chelsea at Old Trafford. Three new signings were secured before the end of the transfer window. Daniel James, Aaron Wan-Bissaka and Harry Maguire joined Solskjaer's team, with the Manchester giants once again in transition.
Lukaku lost his automatic starting role after the Norwegian arrived in December, and his sale was expected after failing to start a game in pre-season. The coach has turned to United's youth prospects to populate his first-team squad, and Mason Greenwood will have starting opportunities after Lukaku's departure.
The transfer window remains open in other parts of the world, with clubs in Spain, Germany and France able to buy players until September 2. Teams in Italy have until August 23 to complete their transfer business. This means United could still see departures abroad in the weeks ahead.
Pogba's future remains in doubt, but United legend Paul Scholes has said fans and team-mates will forgive the Frenchman if he stays at the club.
According to Luke Augustus for MailOnline, Scholes explained Cristiano Ronaldo and Wayne Rooney both wanted to leave United during his time as a player, but both had no problems in the team once they showed their commitment on the pitch.