"The ones who have been linked all look like they are capable of playing for United," he told Manchester Evening News.
"The three linked the most with United are all great top players. Of the three Modric, when we've played against him, has been the one I have been most impressed with.
"Whenever we played Tottenham, he was the one who stood out."
He added: "But there are no guarantees. You could sign Sneijder for £35-40m and it might not work out. He went to Real Madrid and it didn't quite work out for him there, so you just don't know."