Scans on Friday revealed Flores has a slight tear to his left hamstring, which he suffered in the second half of last Monday's win over Sydney FC at the Sydney Football Stadium.

While the prognosis is a blow for the top of the table Reds, the FIFA Match Day Break this weekend has come at a welcome time, as Flores will have longer to recover, before United next takes to the field on October 17 against Gold Coast United.

Reds football director Michael Petrillo says coach Rini Coolen will not play Flores unless he has fully recovered from his hamstring injury.

"Flores will be reassessed after the Gold Coast game next week, but Rini has made it very clear unless he is 100 per cent fit, he won't play," he said.

"So it all depends how he progresses with his rehab over the next couple of weeks."

Flores was a late withdrawal from the Reds' opening game of the season with a leg injury, but the Argentine has started in all eight of the club's fixtures since.

The former Union Santa Fe midfielder has been one of the standouts of the Hyundai A-League's season six, with his South American flair and ability to cut open opposition defences, while he has also scored two quality goals.

Notably, United is yet to taste defeat in the Hyundai A-League since Flores made his Reds debut in the penultimate round of last season.

But while Flores will miss the Reds' next game, Coolen is confident his squad has the quality and personnel to continue achieving results.