Agu pulled up sharply in the closing stages of the Malaysia Super League match in Alor Star after chasing a ball on the left wing.
The burly frontman is due to be checked by the team doctor on Monday, although LIONSXII assistant tactician Kadir Yahaya has hinted that the player could be sidelined for up to three weeks.
"He will have a review on Monday, but for the KL game, I would say he's almost certainly ruled out," Kadir was quoted as saying by The New Paper.
"But it's no big concern for the team - we have a big squad with many others capable of filling his role up front.
"(Khairul) Nizam is ready to play and is likely to start up front."
Although Agu looks set for a spell on the treatment table, central defender Safuwan Baharudin is poised to start against KL at the Jalan Besar stadium on Tuesday evening,
The lanky defender missed his side's battling 0-0 stalemate against Kedah after picking up a knee injury in the match against Kelantan on January 10.
While his teammates travelled to Alor Star over the weekend, Safuwan participated in training with the Courts Young Lions in Singapore and even featured in the last 15 minutes of Sunday's friendly clash against the H-TWO-O Dream Team.
"I wanted to gain some match fitness while the team were away," he said.
"The injury wasn't very serious, it was just a bad knock. I should be able to start against KL if the coach needs me."
"I asked (Young Lions) coach Robin Chitrakar to let me play the last couple of minutes, just to gauge my recovery."
"I felt no pain, there was no problem."
Safuwan's impending return to the LIONSXII first team fold will pave the way for vice-skipper Hariss Harun to revert back to his more accustomed central midfield position.