The Durham seamer has been included in England's 13-man squad for the fourth Test against Australia, which begins on Friday.
Onions has insisted that he is ready to play if called upon.
"I'm champing at the bit and I'm excited," BT Sport quotes Onions as saying.
"I feel ready, I'm delighted to be here, delighted to be part of the squad. If you're in the squad then you're up for selection, you've got a chance of playing.
"I was disappointed not to be involved in the squad for the last game, but to be here at Durham, where I've played all of my cricket and to be from the North-East, [I'm going] to be very proud to put that England shirt on."
Onions has made nine Test appearances for England, taking 32 wickets.