Austin was left out of Southampton’s squad which faced Arsenal at the Emirates Stadium, despite scoring the winner on his debut against Manchester United at the weekend.
And Koeman says that the new boy’s exclusion was due to the fact he struggled through training earlier in the week, due to injury.
"He didn’t have a good session on Monday and if you know his past he was five weeks out and I prefer to wait one week more and then we have the player back," Koeman said.
“It was risky to take him to the squad. It’s not a serious injury and normally he will be available for the weekend.”
Austin’s persistent injury problems have plagued him so far this season, and he did not play much for Queens Park Rangers over the early part of the season, as a result.
Austin only made 12 starts for QPR before moving to Southampton, but he still managed to rack up 10 goals.
The 26-year-old’s absence did not seem to affect Southampton’s performance too much at the Emirates Stadium, either, as they picked up an impressive result.