Martinez left the Swans to take over at Wigan last year and Swansea captain Garry Monk admitted that there was still a bitter feeling from their side.
"Roberto preached a lot about loyalty but ended up walking out," said Monk.
"I'm sure he meant it at the time, but that's why a lot of people, especially the fans, were so unhappy and really felt let down.
"The biggest disappointment was that we all felt we were on the verge of achieving something special for this club.
"These things often take three years and some of us felt he could have stayed that final year to do that with us.
"I'm sure the wages were a big factor and you can understand that was a chance for him to go to the Premier League - but he could have done that with us."