Koeman, however, said the Saints must be prepared for life without the Senegal international, while urging the fans to enjoy his performances while they have him.
"Maybe one day we will lose Mane but then we have to be prepared," the Dutchman said, quoted by the Daily Echo.
"You know in our situation that kind of player, if they play like today, there will come a lot of interest in the end of the season, but now we enjoy watching Mane in our team," he added.
Mane's display against the champions drew plaudits from his manager and consigned Chelsea to their fourth defeat in eight Premier League matches, leaving manager Jose Mourinho grim-faced after his heaviest home defeat in the league and insisting that he was not ready to quit.
"Of course to win against teams like Chelsea you need your best players on that high level and Sadio was very dangerous in his movements," Koeman said.
"It was impossible to have a good defending against him.
"I think the whole team performance was perfect."
Saints midfielder Dusan Tadic agreed with his manager's assessment, saying it showed the team could beat "everyone" in the league.
"It was a really open game and I think we show second-half how we can play good football and in the end we deserved to win," the 26-year-old said.
"But also I think just the way how we play was really important, because if we keep playing like this we can beat everyone."
Southampton welcome fifth-placed Leicester City when the Premier League resumes on Oct. 17 after the international break, while fifth-from-bottom Chelsea play fellow strugglers Aston Villa at Stamford Bridge, before visiting Dynamo Kiev in the Champions League on Oct. 20.
The Ukrainian champions currently top Group G ahead of FC Porto on goal difference. The English champions are a point behind in third place.
(Reporting by Simon Jennings in Bengaluru)
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