We've allegedly had a second bid for Tierney rejected because we didn't offer £25m up front; we've offered £17.5m + £7.5m in add-ons and bonuses providing we get into the Champions League. Celtic, understandably, were not convinced by this.
If we can't even agree a transfer fee for a left-back in the Scottish league, I don't know how the club, or Zaha, can possibly think we can buy a Premier League club's best player who's got a long-term contract with them and have no pressing need to sell. Unless they drastically reduce the price or unless we give them a player or two + cash in exchange, it is hard to see this going through.
As you say, it could be for the best if this doesn't happen. I like him as a player, but I don't want him if it means we lose a 30 goal per season striker in exchange. Nor do I want him crippling our Champions League standard wage bill even further when we're a Europa League club.
He's soon to be 27 and will expect a substantial wage increase. His pace is inevitably going to wane over the next few years. In theory, he could be earning ridiculous money with us until he's in his 30s whilst barely contributing. Which is the problem we've got now, with players who have no resale value, earning top dollar.
I agree we need to sort out the defence, and I still maintain we need a winger too, but under these circumstances, I do not want Zaha.