“I'm worried about him because the one thing United don't want is Liverpool to get above us,” said Ferguson, the most successful manager in Premier League history.
Klopp, who led Borussia Dortmund to two Bundesliga titles and a Champions League final, took over from Brendan Rodgers in October and was charged with breathing life into a team that had struggled for consistency.
The charismatic, 48-year-old German has made an impressive start, with the team winning seven of his first 12 games in all competitions.
Liverpool are seventh in the Premier League, six points behind fourth-placed United and nine behind leaders Leicester City.
Despite the weekend Premier League 2-0 defeat by Newcastle United, Ferguson said Klopp was rejuvenating Liverpool.
“He's a fantastic personality, with those big white teeth always showing,” Ferguson said. “Even at Newcastle when they lost the second goal he goes over to Steve McClaren to congratulate him. That's class, that. And the work he did at Dortmund.
“I know him quite well from the coaching seminars. He's going to make a difference at that club with his personality, drive and knowledge. Things are looking up there.”
Ferguson also spoke up for Chelsea manager Jose Mourinho who has endured a torrid season so far, losing eight of their 15 games including a 1-0 league loss at home to Bournemouth on Saturday.
“There is no point in sacking one of the best coaches of all time; he's won the European Cup twice, he's won the league in each country he's managed in,” Ferguson said.
“It would be foolish to take that step to sack him. That would be bad management. It's not leadership.” – Reuters
Original source: Klopp worries Fergie