The Serbia playmaker set an impressive early pace in the first half of his debut season at Southampton, but struggled to cope with the relentless winter schedule.
Tadic has vowed to learn from the spate of injuries he suffered at the tail-end of last season, as he adjusted to his first campaign without a winter break.
Saints boss Koeman is impressed by the 26-year-old's resolve, but admitted the jury will be out until the new year on whether he can stay the course this term.
"I think it's too early to judge that," Koeman said.
"At this time last year Tadic was fantastic and he was starting with physical problems in December, January.
"Wait until January and ask me again."
The international break that follows Saturday's trip to Sunderland will be the only respite before the hectic Christmas schedule.
Former Holland defender Koeman believes he will only need to make minor tweaks to his selection policy to cope with the Premier League's rigour this term.
The Southampton boss did, however, insist that he will be selective when it comes to resting his top stars, challenging his squad to dig in when the season grinds past the halfway point.
"First of all I've made more changes in the Capital One Cup," said Koeman.
"And I'm not a fan of making a lot of changes every week.
"Sometimes I'll leave one or two players out to give those players a rest, because I've learned also from last year."
Source : PA