The young fullback has had no luck during the past two years but did well on his comeback match.
McMahon told the Evening Gazette: "All I want to do is to get back playing football again.
"I feel quite fit and now I have to keep pushing on and challenge Luke Young.
"I am a determined lad. I want to play in the first team.
"The manager has brought players in and it's right that he should look for competition for places.
"It's up to me to play well enough to give the manager a problem."
McMahon also thanked team-mates Robert Huth and Jonathan Woodgate, plus fitness expert Nick Allamby, for their contribution in helping his return to action.
He said: "They've all been brilliant to me and helped me to get through it and get fit again."