Other doubtful starters for the grass court Grand Slam include Victoria Azarenka and Jo-Wilfried Tsonga.
Former Wimbledon champion Rafael Nadal says he will not be playing at this year's Grand Slam tournament due to a wrist injury.
The same injury forced the Spaniard out of the French Open Grand Slam.
In a statement on his Facebook page, Nadal said, "I would like to tell you that after consulting my doctor and given the results of the last medical checks, I will not be able to take part in the next edition of Wimbledon.
"As you can imagine, it's a sad decision but the wrist injury I suffered at Roland Garros needs time to heal."
Twelfth seed Jo-Wilfried Tsonga's preparations for Wimbledon have suffered a massive blow after he was forced to pull out of next week's warm-up event at Queen's Club in Nottingham, West London.
The Frenchman sustained an adductor injury against Ernests Gulbis in the French Open third round and has been unable to recover in time.
In a statement released by tournament officials, Tsonga said, "I am very disappointed that this injury means that I will not be able to play in the Aegon Open at the Queen's Club.
"It is one of my favourite tournaments, home of some very happy moments for me on the court - reaching the top 100 for the first time and playing in the final - and I was looking forward to coming back. I hope to return in the future."
Fifth seed Victoria Azarenka has been forced to pull out of the Aegon Open due to a knee injury.
The knee injury caused the Belarusian to retire from her first-round clash against Karin Knapp at Roland Garros.
She said, "I am very disappointed to have to withdraw from Nottingham. My knee is unfortunately not yet completely healed and ready to play at 100 per cent. I had been very much looking forward to playing here in front of the fans in Nottingham but hope to have a chance to come back next year instead."
The Aegon Open is the traditional grass court warm-up event to Wimbledon.
Many players generally miss this competition to heal any injuries as they head to Wimbledon, which is the oldest tournament in the world.
Wimbledon is played on all grass courts, which makes it extremely demanding.
It is one of four Grand Slam tournaments which take place in a tennis year.
The tournament takes place from June 27 to July 10 at London's All England Club.