Chelsea have two targets: Frenkie de Jong and Bernardo Silva. However both of them are very tough ones. Frenkie de Jong is likely to be kept by Barcelona this summer but there is still a slight chance for a possible transfer. As for Bernardo Silva, Manchester City aren't thinking about selling him now. He is important for his team and they wouldn't even want to sell him to a rival team I guess. Therefore Chelsea had better have some backup plans.
For Frenkie de Jong Barcelona, it has confirmed not to sell this season, differently with true Silva the opportunity to be purchased is far more open to now, depending on the agreement offered by Chelsea, in football there is no term not to sell to the opposing club, because the player which is released or purchased is very dependent on the agreement, advantages and demands of the player itself, but the backup plan is needed by Chelsea, if the two players still survive in the old club, then they have the choice of other players to be purchased
Bernardo Silva to Chelsea seems only remains rumours because currently he linked to Barcelona even he wouldn't consider the offers from other clubs besides Barcelona because he interested want to play under Xavi strategy and reported he already had personal agreement with Barcelona regarding this transfer but Silva have to wait until the end of this transfer window because Barcelona want to ensure Frankie De Jong status first whether he will decided to stayed or leave