According to The Mirror, the Belgian international had surgery on his left Achilles on Monday, with the initial prognosis ruling him out till at least November.
This news is likely to give Arsenal manager Arsene Wenger a further headache, after it was revealed earlier this week that young playmaker Jack Wilshere will be out injured for up to three months.
It has also been revealed that Vermaelen's latest injury is not on the same leg which previously troubled the Belgian centre-back, and ruled him out for most of last season.
For now, neither Arsenal nor the Belgian national team have confirmed these reports.
However, if true, it could come as a huge blow to the Gunners' aspirations for the rest of the season, even at such an early stage in the campaign.
Vermaelen scored eight goals in 45 matches in his debut season at Arsenal, but only managed five games last term.