Great Britain defender Ifeoma Dieke will miss the rest of the Olympics after suffering knee ligament damage.
The 31-year-old picked up the injury in the second half of Saturday's 3-0 Group E victory over Cameroon in Cardiff.
It happened after a tangle with Cameroon's Ajara Nchout and the extent of the injury was revealed after a scan on Sunday.
Chelsea defender Dunia Susi will be brought in, subject to International Olympic Committee clearance.
Dieke was one of two Scottish players in Hope Powell's squad of 18 along with forward Kim Little and she had formed a successful partnership in the middle of defence with skipper Casey Stoney.
GB have yet to concede a goal at the Games after and following that up with the victory over Cameroon that secured their passage through to the quarter-final stage.
They will conclude their group campaign with a match against heavily fancied Brazil at Wembley on Tuesday, a game that will be played in front of more than 70,000 spectators.
Sophie Bradley, who plays alongside Stoney for Lincoln Ladies, replaced Dieke on Saturday and is likely to start when GB face Brazil.
The Brazilians defeated New Zealand on Saturday to join GB in securing qualification from Group E - and their encounter will determine who finishes top of the group.
The importance of finishing first cannot be under-estimated because that team will take on a side third in either Group F or G in their last-eight tie.
In contrast, the team that comes second in Group E will face the runner-up of Group F, which is likely to be either Sweden or Canada.