Babblelot said:
If someone in the main entry withdraws, is that slot necessarily replaced by a LL, or could, say, the US Open give Andrew Murray a W/C?
If a WC from the main draw withdraws, they could give it to someone else. This is what happened in Cincinnati - Murray got Fish's WC when he pulled out.
If a non-WC entry withdraws, then who replaces him depends on when he pulls out. If it's prior to the start of qualifying (it might have to be prior to the quallie draw coming out, I'd need to check the rules on that), then the next on the main draw alternate list will get in. Often that player would have been entered for the qualifiers, so a replacement is also required in the qualifying competition too (from the qualifying alternate list).
If the withdrawl happens after quallies have started, then an LL will be added into the main draw, but not necessarily at that position - if the qualifiers haven't yet been placed in the draw, then the LL may get any of the LL/Q spots when they are placed.
Babblelot said:
With respect to LL, do you have to reach the final round of the qualies? For example, say Murray lost in 2R of a qualifying match, could he still be given a LL?
Not necessarily - I think someone got into a tournament the other week who had lost in the first round of qualifying. Those who have lost in the final round of quallies are considered first, in order of entry ranking, and if none of those guys are available (some just move on after they've lost), then the losers from the previous round are considered.
There are 16 Q spots in a Grand Slam draw, which means 16 3rd round losers. So for someone to be considered from the 2nd rnd, it would mean that there would have to be an awful lot of withdrawls from the main draw, or 3rd rnd quallie losers unavailable. That said, if Murray lost in the *3rd* round of quallies, as one of the highest ranked players in the draw, he'd have a very good chance of getting a lucky loser spot.