Barcelona has to make sale of Frankie De Jong before they can make a good bid for Lewandoski. Lewandoski is ready to wait for offer's from Barcelona. The deal between man United and Barcelona would be done for de Jong. Then they can have enough funds to bid for Lewandoski and possibly another player. Barcelona did good last season ever since Xavi took over the job.
That seems to be what they were planning behind selling Frenkie de Jong. Yes, they will use that profit to buy another player, namely Lewandowski, whom they have been eyeing for all this time. But Barcelona must prepare a replacement for the player who played regularly last season. But if they are a little late to sign Lewandowski, they could lose him too, because now rumors about a team being interested in Lewandowski are getting louder.