Wimbledon's strict all-white clothing policy has forced John Millman to send his father on an emergency undies run.

Millman was preparing to face Milos Raonic ahead of his second-round defeat, when officials informed the Australian his underwear was too bright for his shorts.

It required his father Ron, known as "The Fox", to dash to a local shop to find something suitable to meet the All England Club's tastes.

"I don't know where he got them from, but he walks everywhere. He walks here every day from Clapham," Millman told AAP.

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"The Lotto pants this year are really thin, which is good for us, it feels like you are playing naked out there.

"I shouldn't say this, but I have worn those undies, or similar types, for the last few years."

Millman went onto lose to Raonic in three straight tie-breakers 7-6 (7-4), 7-6 (7-4), 7-6 (7-4).