Theres so many problems with buying a new LB. One is that I dont think we need one as Robinson has proved he is capable in the same way Ashley Cole proved when he was at Arsenal. Buying a new LB puts him in 3rd choice and means we would have signed 2 of them in the last 2 years. That doesn't give Jack any time to break into the first team.
The other problem is that our defence is not our problem, its our attack. We dont score enough goals and thats where the large majority of our transfer funds should go too. Wasting money on a new LB would be stupid as it would be put to better use in funding for the winger and striker we desperately need.
If we only signed 3 players this transfer window it would be ok. A clinical striker, like Gomez or Huntelaar(obviously not those 2 in particular) a left winger as I'm sure Suarez will be on the right wing next year and also a competitor for the DM role for Lucas, we need a massive upgrade from the current replacement that is Spearing.
Goals from midfield are also a problem which is why we need someone like Gylfi. 4 players max is all we will sign this window. The suggestion that we sign 6 players, as someone else said earlier, 2 of them in defensive positions, is crazy.