Olympic squad members Crista Cullen, Alex Danson and Sarah Thomas will miss the Investec London Cup because of injury.
Leicester duo Rebecca Herbert and Kerry Williams and Susie Gilbert of University of Birmingham have been drafted in as replacements.
The squad for the London Cup has 18 players rather than 16 in the Olympic squad so 2012 reserve players Abi Walker and Natalie Seymour will be involved in Chiswick.
Great Britain begin their campaign on Tuesday afternoon against South Africa and then face Germany on Thursday.
Great Britain head coach Danny Kerry is pleased with the replacements and looking forward to welcoming Cullen, Danson and Thomas back in time for the Games.
"Beckie, Kerry and Susie will replace Alex, Sarah and Crista who are making good progress in their rehab in time for the Olympic Games," he said.
"The three replacements understand our play well and bring good energy and pace to the team."