Pretty sure Kroos' sign-on bonus, if he joins United on a free next season, would easily make up for one more year with lower wages in a team fighting for the CL title. Usually both the player and the new club benefit financially from a free transfer, after all the available money has to go somewhere and the former club gets feck all then
. The question is can United afford to wait? How important is Kroos or are there different players worth buying this season and Kroos could be the icing on the cake next season? Bayern doesn't need the money and are happy to keep Kroos one more year, especially now that Thiago is injured again and might miss the pre-season.
For example:
Bayern were in desperate need of a new goalkeeper, Neuer was available and it wasn't clear that he definitely would wait one more year for the big move (even though he stated later that he only wanted to join Bayern). So we were forced to pay 25m for a goalkeeper with only one year left on his contract.
With Lewandowski, we weren't desperate. So Dortmund couldn't push the price too high and we were comfortable waiting another year. Lewandowski got a small raise to perform well for Dortmund, probably gets a big sign-on bonus from us now and probably made overall more money by staying one more year in Dortmund than by being sold last season.