Top 10 players Daniil Medvedev and Stefanos Tsitsipas have confirmed they will play at Queen’s in June.
Spain’s defending champion Feliciano Lopez will return, while organisers hope Britain’s Andy Murray will recover from a pelvic injury in time to play.
Former world number one Murray, a five-time champion, has not played since November’s Davis Cup finals.
Three-time Grand Slam champion Murray was forced to pull out of January’s Australian Open because of the pelvic injury.
The 32-year-old said last month he was not putting a time frame on his recovery as “bone bruising” is taking longer to heal than expected.