The former Peterborough and Norwich star, who was played on the wing at times by boss Chris Coleman to good effect, suffered thigh and Achilles problems and seriously thought about calling it a day.
But after deciding not to hang up his boots, McKenzie is raring to go in pre-season and throughout the course of the forthcoming Championship campaign.
He told the Evening Telegraph: “I ruptured my thigh earlier in the season and got back from that and then within a few months I did my Achilles. It was mentally traumatising.
“I was seriously thinking about retiring, but I had a chat with my family, Chris (Coleman) and a few people and changed my mind.”
He added: “I have had a lot of bad luck with injuries but I am a fighter and I realised that I still have so much more in me and I am ready now.
“I am looking forward to getting back to my best and scoring goals for the team.”
Mohamed Salah continued his astounding goalscoring form on Saturday, hitting four goals as Liverpool thrashed Watford 5-0 at Anfield.
A goal apiece from James Tomkins and Luka Milivojevic handed Crystal Palace a crucial 2-0 win over Huddersfield at the John Smith's Stadium on Saturday evening.
Manchester United bounced back from their Champions League exit as they beat Brighton 2-0 at Old Trafford on Saturday night to reach the FA Cup semi-finals.
Tottenham reached the FA Cup semi-finals after they cruised to a 3-0 victory over Swansea in their quarter-final clash at the Liberty Stadium on Saturday.