Manuel Pellegrini says he could not believe Manchester United lost 7-0 to Liverpool on Sunday.
Real Betis boss Pellegrini will lead his side against United in Thursday's Europa League last-16 first leg at Old Trafford.
The 69-year-old Chilean spent three seasons in charge of Manchester City between 2013 and 2016.
"It really was unbelievable," he said of United's defeat at Anfield.
Pellegrini watched the first half of the game before he had to concentrate on his own side's encounter with Real Madrid, which they drew 0-0.
"I missed the other six goals but I understood immediately what would happen," he said.
"Because of the rivalry [with Liverpool] and this amount of goals, I knew it would not be easy for them.
"But I was not very sad about what happened. I am a Man City fan as well."