The Spaniard sustained the injury during the 4-2 defeat to Chelsea at Stamford Bridge last Saturday and was replaced at half-time by Argentina centre-back Federico Fernandez.
Amat underwent a scan on Sunday and saw a consultant the following day, with the results confirming a strained lateral ligament and ruling him out until the end of October
The 22-year-old has started all four of Swansea's Barclays Premier League matches to date but his injury will now allow Fernandez to establish a central defensive partnership with captain Ashley Williams
Fernandez, who played four times for Argentina at the 2014 World Cup, has only made one start for Swansea since his £8million move from Napoli last month, the Capital One Cup home victory over Rotherham
Source : PA
Source: PA