This week the London Queen's Club tourney is taking place, the round of 32 started on Monday June 18th 2018.
Stan Wawrinka is currently ranked ATP #261, and Andy Murry is ranked ATP# 156
According to the Draw (PDF) the "Last Direct Acceptance" is Ryan Harison with ATP #59 rank.
Why are Wawrinka and Murray allowed to play without a wildcard if their ATP ranking isn't high enough? They also don't marked as PR (Protected Ranking).
To enter a tournament at the ATP level the ranking 6 weeks before the Monday of the week of the tournament is relevant. Therefore, for Queen's the ranking of 07.05.2018 is relevant. At that time Murray was ranked #39 and Wawrinka was ranked #25, both good enough to get directly accepted into the main draw. See the entry list here.
See in the rulebook at 7.13 Selection of Entries / A. Singles Main Draw / 1) Direct Acceptances.
Direct acceptances are players accepted directly in the draw by virtue of their position in the ATP Rankings or by their protected ranking position (singles). The list to be used for ATP World Tour tournaments shall be dated approximately forty-two (42) days prior to the Monday of the (first) tournament week and twenty-one (21) days prior to the Monday of the tournament week for ATP Challenger Tour tournaments.
