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.
I want to know which other team wants Lewandowski, indeed all the teams currently want Lewandowski but in reality Lewandowski only wants to play for Barcelona. Lewandowski himself wanted a salary increase at Bayern Munich but unfortunately Bayern Munich did not agree to that, which is why Lewandowski was so adamant about leaving and the team he wanted was only Barcelona and no other team. Although there have been rumors of interest from other teams, those rumors have always included a refusal from Lewandowski.
For now it is only Barcelona he shows interest of playing for and Barcelona is the only big team that is really in need of him. If other top teams maybe later want him , Barcelona may loose their chances of having him . Since Barcelona are still interested in buying that means they may end up succeeding in getting him from Bayern Munich.