Millwall midfielder Danielle Carlton has learned she has a chest infection after suffering chest pain in Sunday's Women's Super League loss at Everton.
She left the field on a stretcher in the second half and was taken to hospital in an ambulance.
The former Brighton player was cleared to leave hospital on Sunday after a series of tests and she will have further tests in London on Monday.
Millwall physio Jonjo Hurley said the Everton medical team were "fantastic".
Carlton, a former Gillingham and Charlton player, joined the second-tier side from Women's Premier League South club Brighton in April.