Former United star Coppell has been blown away by his former side's explosive opening to the new campaign, which has seen them romp to five successive league wins.
Coppell cannot see past them retaining their crown as English champions but the 56-year-old described Barca as "way out in front" of all of their rivals when it comes to the Champions League, which has seen them beat United in two of the last three finals.
"Looking at it now, United v Barcelona, if you ask me, I'd say Barcelona will win, because they are irresistible," Coppell told Press Association Sport.
"The football they play on a week-to-week basis, I would suggest, is very difficult to beat.
"There will be a way to beat them, and once it is well-known, they will be closer to the pack.
"But, at the moment, they're way out in front.
"I wouldn't be surprised if Barcelona play Man United in the European Cup final again this year because the two of them do look to be far and away the best in Europe."
Indeed, Coppell, who played for United between 1975 and 1983, was confident Ferguson's youngsters would prove too strong for their domestic rivals.
"You look at the squad Alex has developed and it just looks to be exceptional," he said.
"I've yet to see the confrontation with Man City but, in terms of the depth of squad United have, I can't see them falling."
Former Crystal Palace boss Coppell still backed City - who he walked out on after just 33 days in charge back in 1996 - to be United's closest challengers.
"Alex called them the noisy neighbours," he said.
"But now they're beginning to walk the walk.
"All of a sudden, it's a head-on battle across the city.
"It'll be fascinating to see the first derby this year to see who comes on top."
That first derby is on October 23, a fortnight before Ferguson celebrates a quarter of a century in charge of United.
"His drive, even now, has been incredible," said Coppell, speaking at the launch of '19', a book by award-winning journalist Harry Harris which chronicles each of United's record-breaking 19 league titles.
"I think he gets reinvigorated by forever chopping and changing the team, bringing new elements to the side.
"It's easy for a manager to become complacent, but he never does.
"The joy for every goal they score is apparent when you watch him on the sideline, the pain of every goal conceded."
Coppell, who was manager of Crystal Palace when United beat them to win the 1990 FA Cup - Ferguson's first trophy at Old Trafford - believes the 69-year-old still has plenty of years left in charge.
And he insisted there would be "a queue a mile long" to replace him when he finally retires.
'19' by Harry Harris is the story of Manchester United's league championship record.