Sears coaches Ana Ivanovic and was watching her match with Madison Keys on Rod Laver Arena.
The match was suspended for an hour before resuming.
Murray is unaware of what has happened, and is currently continuing his third-round match with Portugal’s Joao Sousa.
Andy Murray’s brother Jamie told reporters Sears, 58, who has been taken to hospital for tests, was “conscious, talking and sitting up.”
Sears’ daughter Kim is not in Melbourne in support of Murray as she awaits the birth of their first child in a few weeks.
Sears is in his second spell working with Ivanovic after he was reappointed the Serbian’s coach in July last year.
He has previously worked with Daniela Hantuchova and Amanda Coetzer and was also captain of the British Fed Cup team.
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