The pair came through the ranks together at Anfield.
And Gerrard told FourFourTwo magazine: "I don't like it. It's weird and doesn't look right.
"I played with him in the red of Liverpool since I was 10, so to see him in the red of United is difficult for me.
"Obviously it was a chance he needed to take so I wish him well personally - but I do not want United to do well at all."