Austin, who has scored almost half of the Saints' paltry 14 goals in the Premier League this season, faces surgery on the shoulder he dislocated in last Thursday's Europa League draw with Israeli outfit Hapoel Be'er Sheva.
"Normally he needs surgery and will be perhaps between three months and four months (out)," said Puel after his side's 1-0 win over Middlesbrough on Sunday.
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"It's a good estimation for the time after the surgery. Is it dislocated? Yes I think. Will it need surgery? Yes, normally yes".
Austin's absence will place the burden on experienced Irish international Shane Long and their record signing Sofiane Boufal, who opened his Premier League account with a superb strike against Middlesbrough.
