Monfils beat Golubev in three sets despite the injury
France's Gael Monfils and Russian Marat Safin have withdrawn from the Aegon Championships at Queen's Club with wrist and back injuries respectively.
Monfils' injury, picked up in his second-round win over Andrey Golubev, means Belgium's Steve Darcis will progress to the last eight on a bye.
The world number 14 has decided to rest the injury ahead of Wimbledon.
Safin had already received a bye in the first round and was due to play Xavier Malisse on centre court on Wednesday.
The world number 20, who was ranked number one in late 2000 and early 2001, became the first Russian to reach the semi-finals of Wimbledon, in 2008.
South Africa's Rik de Voest, a lucky loser from qualifying, replaces Safin.
The Russian who has won the US and Australian Open Grand Slam titles, plans to retire at the end of the season.