Cousins gets run out in Wales.
Mark has had to wait patiently in recent weeks, with loanee shot stopper Sam Walker making the goalkeeper berth his own since his arrival from Chelsea.
He will turn out against the Swans at the Liberty Stadium, alongside fellow first teamer Matt Heath.
The U21s will be without Alex Gilbey, who is currently out on loan at Newport County. Alex played in County's game on Saturday, but was back on the bench for their win at Nuneaton on Monday.
Jordan Sanderson and Freddie Ladapo will also face the Swans in a strong looking U's squad.
The game at the Liberty Stadium kicks off at 7pm.