The two teams have been pitted together for the round of 32 tie.
"It is clear that I return home, where I have grown as a player, but my heart is now in Real Sociedad and I am going to do my best to get us through. I'm from La Real and I'm very happy to be here," said Januzaj.
"We are playing very well for the moment. We have a young team, but with a lot of quality. We have David Silva, who gives us maturity in the game, Nacho Monreal, both have played before in the Premier and they know what it's like to play there.
"It will be a difficult game for us, but for them too, and we will try to win as usual."