The Pole is convinced Sneijder has taken Inter's game to a new level and is proving Real Madrid were wrong to dump him.
"At the beginning of the season, I predicted that the Nerazzurri would win the Scudetto and they are proving me right," said Boniek.
"However, without Ibrahimovic, I expected more difficulty for Mourinho. Instead the quality of the group has increased and we are even starting to see some beautiful football.
"The signing of Sneijder in the last days of the transfer market has been decisive. Inter have become the perfect team with Sneijder.
"Then I ask myself: Do Real Madrid regret selling him so easily?"