Ayala, who has made just two league appearances since October because of injury and limped out of the 2-0 defeat at Stoke on March 4 with a hamstring problem, has returned to training and is in contention to play at Vicarage Road.
Uruguay striker Cristhian Stuani is also available after recovering from his exertions on international duty, but defenders George Friend (calf) and Calum Chambers (foot) are still out.
Swansea (from): TBA
Middlesbrough (from): Valdes, Guzan, Barragan, Fabio, Gibson, Espinosa, Ayala, Husband, Fry, De Roon, Clayton, Forshaw, Leadbitter, Guedioura, Downing, Stuani, Traore, Fischer, Negredo, Gestede, Bamford.
