Salgado said: 'Manchester United are missing Cristiano, that's for sure. Anyone would miss a player like him. But they can't afford to think about him and the past. In football there is no past, only the present.
'Cristiano has to think about Real now because I've told him the first year will always be a difficult one.
'It will be a very difficult year for him and the rest of the new players, but I said to him that if you can get through the first year, you will do great things.'
Blackburn have conceded 16 goals in four away games so far this term and Salgado admits Old Trafford will pose a tough test.
He said: 'Old Trafford is a great stadium which holds some great memories for me. It's a wonderful stadium to enjoy.'