Sir Alex has urged United to "wake up" in European football this season ahead of the Old Trafford encounter with Athletic Club.
The Reds face the side from Bilbao in the Round of 16 in the Europa League, looking to improve on the home showing against Ajax as the Amsterdammers won on the night but lost 3-2 on aggregate.
"It's a very difficult tie," stated the boss. "All the work Bilbao have done has been very impressive. They're a very progressive team in Spain at the moment and it's going to be very difficult for us. We need to waken up, there's not question about that. Some of our European form has been disapppointing.
"But it's an opportunity to progress and we want to take that opportunity, although it's going to need a very good performance."
The manager was honest enough to reflect on the Champions League exit and wonder what may have been the problem, after doing so well to reach three finals in four years.
"I don't know if it's because we're making too many changes in these games," he pondered. "Certainly against Ajax in the second leg we did that. We also made mistakes in the group stages. It's our own fault. The Basel game will always be remembered for the carelessness of our performance.
"We were a bit unlucky against Benfica at home but, at that point, we needed to beat them. It was a disappointment but tomorrow I'm playing a strong team and I hope that makes a difference."