(Reuters) - A Swiss goalkeeper has threatened legal action after fans of a rival lower league team urinated in his water bottle and then taunted him when, unawares, he took a sip during a match at the weekend.

FC Muri goalkeeper Reto Felder said he had felt sick after tasting the warm contents of the bottle, which he had left near the goalpost during the 1. Liga (third tier) game at FC Baden near Zurich.

"The idea of drinking piss is simply intolerable," the Aargauer Zeitung website (www.aargauerzeitung.ch) quoted the 34-year-old player as saying, adding that he was waiting for an analysis of video evidence before further action.

"What if next time it is something that knocks you out?," added Felder.

Swiss tabloid Blick reported that the unidentified fans had persuaded a ball boy behind the goal to pass them the bottle during the second half of the match.

The paper said the fans shouted "Now you have AIDS" after Felder realized what had happened.

Muri coach Beat Hubeli was shocked

"That's bottom drawer," he said. "I've played football and experienced a lot but that beats everything."

Baden president Thomi Bram apologized to the goalkeeper on the club website (www.fcbaden.ch) and said they were conducting an internal investigation.

Condemning the fans for damaging the club's reputation with their 'reprehensible' behavior, he said he had apologized in person to the goalkeeper, coach and Muri president and informed the Swiss soccer authorities.

(Reporting by Alan Baldwin, editing by Ed Osmond)