The Dutch youngster's arrival has been criticised by some pundits.
"Luc is showing us some really excellent things in training where he is playing very well," Sneijder commented.
"However, he's lacking a bit of luck in the games themselves where he seems a bit stuck.
"Nevertheless, that is only normal for a youngster who finds himself playing at a great club. Luc has demonstrated that he is a very good player."