McClaren was asked about United signing ex-players of coach Erik ten Hag.
This summer, United have brought in Noussair Mazraoui and Matthijs De Ligt, who were both at Ajax with Ten Hag.
“First, (the players know) the way he wanted to play. Two, the players that were available. Three, knowing he didn’t have a lot of time at United to get things going,” McClaren told the Telegraph.
“(Lisandro) Martínez at the beginning, (it was a case of) are you sure? Yes, he (Ten Hag) was. Because he (Martínez) knows the way Erik wants to play. I have done the same as a manager.
“Going into a club trying to instil something, I always wanted two or three I have worked with previously. You need followers and people who believe in what you are doing. There is a list of five (potential signings) and you pick the one that you know.”