The Brazil international has struggled to win over his manager Antonio Conte but has cemented his place as an automatic starter following a superb run of form which has seen him score five goals in his last five appearances.
Willian scored the opener and hit the post twice during an evenly contested first leg which ended 1-1 at Stamford Bridge a fornight ago.
‘We have to pay special attention to him [Willian],’ said Busquets.
‘But Morata, Pedro or Hazard. They have specific attack profiles. They are a good team.’
Head coach Ernesto Valverde added: ‘Not only in the first leg, he has been playing really great with Chelsea and finding the back of the net.
‘With those players with that quality, that find shooting easily. He is in the best form of the season.’
Antonio Conte deployed Eden Hazard as a false nine in the first leg but could revert to the 3-5-2 system which saw Chelsea beat Atletico Madrid away from home in the group stages.
However they line up, Valverde believes Chelsea will provide stern opposition, despite the odds being heavily stacked in Barcelona’s favour.
‘I don’t know what will happen tomorrow. They have a lot of different ways of playing. They did that in London in the middle of the game.
‘If they take a step back they have some very good individuals. We will try to beat them in any case. To keep playing and trying.
‘We can’t be on top of them for the whole match. They have the most counter attacks of the Premier League.’