"If the right player comes along, you have to be prepared to make a move," Ferguson said.
"I can find room for anyone here if they have the right quality. I am not sure Lewadowski will be sold to Bayern now. The Dortmund fans are not going to be happy and I don't think they will sell to their main rivals.
"I think they will either let his contract run out, or sell him somewhere else."
Ferguson was in Dortmund this week to watch their game against Madrid, although it is unknown which players, if any, he went to look at.