If it was a choice between a DM (either Fred or Weigl) in January or Sanchez I'd prefer if we signed a DM. Yes neither would be available for the Champions League but there is a danger Fernandinho could be burnt out by March/ April due to his workload so far. Yaya has nowhere near his mobility.
I think the whole United/ Sanchez is a giant bluff by Alexis to force us to commit to a January transfer, if we don't raise our offer though I wouldn't be surprised if his bluff was called and he went there. They desperately need to get one over us, he would be feted as a saviour over there and they will spend whatever is necessary to buy some credibility. I know he has indicated he wants to play for Guardiola but if we won't pay for him now combined with a plea to his vanity and a shedload of cash could see him going there.