Keegan Bradley and Luke Donald clashed over a little-known Ryder Cup rule that proved pivotal on a dramatic final day at Bethpage Black.

Europe sealed a 15-13 win on Sunday afternoon thanks in part to half a point from Viktor Hovland - despite the Norwegian withdrawing from his singles match against  Harris English. 

Hovland was forced to pull out after aggravating a neck injury and that meant the 'secret envelope' protocol came into play.

Under those rules, which have been invoked only twice since 1979, each captain named one player prior to the singles who they would bench in the event of an injury or illness on the opposing team. Keegan Bradley designated English. 

The extra half-point proved critical as Europe withstood a final-day charge from the Americans. And after the match, Team USA captain Bradley said the rule 'has to change.'

'I think it's obvious to everybody in the sports world, in this room,' he said. 'Nothing against Viktor. But that rule needs to change by the next Ryder Cup.'

When asked how he would tweak the protocol, the American captain added: 'I have a few ideas but I'm not going to tell you right now... the rule has to change.'

When those comments were put to Team Europe during their press conference, Robert MacIntyre laughed and Donald hit back.

'We have contracts for a reason, a captains' agreement for a reason, for situations that occur,' the European captain said. 'The rule is the rule and it's been in place for a long time... I think it's been in place since 1971. The US have used it before. I think it happened in 1991 with Steve Pate. 

'That was a tight Ryder Cup, too, 14.5-13.5. It happened in 1993 - Sam Torrance couldn't play with an injured toe. The US won that one.'

Rookie Pate had sustained injuries during a car crash earlier in the week and, despite having played in Saturday's afternoon session, US captain Dave Stockton deemed him unable to play. He had been slated to face the legendary Seve Ballesteros in the singles.

Hovland, meanwhile, starred alongside MacIntyre in taking down Scottie Scheffler and Russell Henley in the morning foursomes on Saturday. But then he abruptly pulled out of the afternoon fourballs at short notice because of the recurrence of an issue he has battled for two months. 

And on Sunday night, as Europe celebrated their victory, Donald paid tribute to Hovland and dismissed any notion that the rule was used as a get-out clause.

'I would have had absolute faith in him to deliver a point today,' Donald said. 'He couldn't play. He was gutted.'