Vermaelen fell out of favour at the Emirates Stadium last season as Arsene Wenger preferred to go with a central defensive partnership of Per Mertesacker and Laurent Koscielny.
The Belgium international will now be made available for transfer but the Gunners can only expect to receive half of the £10million they paid Ajax for his services back in 2009.
Wenger will use any money raised to fund a swoop for Williams and is ready to make a move despite the fact Swansea insist they are under no pressure to sell and wish to keep hold.
A fee of £12million has been mentioned for Williams and that should not be a problem for Wenger as reports continue to suggest he could have as much as £70million to spend on new players this summer.
Paul Huntington says Preston's play-off hopes this season hinge on them getting the balance right on and off the pitch.