The incident took place on Tuesday when grenade was thrown at a Malayasian restaurant in busy Puchong district. The outburst happened at 2.15 am in the front porch of Movida restaurant.
When the incident occurred, 20 visitors were watching match between Italy and Spain, Euro Cup 2016 when the incident happened, reports said.
"Eight people were injured in the hand grenade attack early Tuesday. One of them, a man, is in serious condition," police said.
"I rule out terror attack. The blast is likely motivated by business rivalry among the local gangsters or a revenge attack," he said.
In 2014, similar attack happened when a Malaysian man was killed and 13 people, including Singaporean, Thai and Chinese tourists were injured, after a bomb exploded in front of a pub in Kuala Lumpur.
Abdul Rahim Jaafar, state deputy police chief, told AFP that the attack on the Movida restaurant in busy Puchong district was probably the result of a business conflict or revenge.