A West Coast Heartland rugby player has had emergency brain surgery in Christchurch Hospital after a medical event at Rugby Park, Greymouth, on Saturday.

Brogan Watt fell ill immediately after West Coast's 62-28 loss to Poverty Bay.

West Coast Rugby Union chief executive Mike Connors said Watt did not feel well at the end of the game and was checked over on the ground by the team's medical staff and St John paramedics, before being taken to Grey Base Hospital.

"The player was flown to Christchurch Hospital on Saturday night where he had surgery on his brain," Connors said.

Watt, a loose forward, was subbed in the second half of the game, and Connors said that was a "tactical" substitution.

"The West Coast Rugby Union is supporting the family the best way we can."

The Greymouth Star understands Watt underwent major surgery on Saturday night when he arrived at Christchurch Hospital, where surgeons removed a piece of his skull to remove a blood clot to relieve pressure on the brain. It is believed the surgery went well, however Watt remains in a coma and in a critical, but stable condition.

Watt has hit his straps on the rugby paddock in recent weeks. Last week against Mid-Canterbury, West Coast manager Mark Costello said Watt had a "colossal game" at flanker.

Watt was everywhere making big tackles in the midfield and carrying the ball up strongly, as well as scoring a try.

He was in top form again on Saturday, before he was substituted, and had a hand in one of the host's tries.

- Greymouth Star