United and Manchester City failed to progress past the group stage of the tournament, while Chelsea and Arsenal face likely elimination in the first knockout round after comprehensive first-leg defeats to Napoli and AC Milan respectively.
However, the 70-year-old is not anticipating a longer-term decline in the influence of English clubs in continental competition.
"Success in Europe can sometimes go in cycles," Sir Alex told reporters ahead of his side's Europa League fixture against Ajax.
"Spain had a great cycle about 10 years ago when Valencia, Deportivo La Coruna, Villarreal, Real Madrid and Barcelona were all dominant.
"There were three of them in the semi-finals the year Real Madrid won it. We've had a great cycle in the Premier League for the eight years, with teams getting to semi-finals and finals.
"And I don't see that subsiding, to be honest with you. I think the English teams will continue to be dominant.
"We've had a bad year this year – we [United] have, in particular - and we can only judge ourselves.
"But with Arsenal and Chelsea, disappointing results though they've had, both clubs have had injury problems and you can't expect them to get the best results without their best teams.
"So it's maybe been a disappointing season, but not really to my mind definite that we're on the slide."
The Scot is hoping that midfielder Tom Cleverley will be able to complete 90 minutes against Ajax after recently returning from injury.
"He's a very clever footballer," Sir Alex said of Cleverley. "He's got a quick brain in terms of his appreciation of passing.
"An hour last week against Ajax was fantastic for him and hopefully he'll pay a full game this time. He gives us more ammunition in the midfield area which, for a few months, everyone was starting to worry about.
"But with Paul Scholes, Ryan Giggs, Michael Carrick and Anderson, who is now back in training, we have some good options."
How do you stay up to date with football when on the move? With http://m.goal.com – your best source for mobile coverage of the beautiful game.