The Owls see themselves out of the top six after a good run prior to many of their key players picking up injuries.
But McMahon, back from a knee injury himself was making his first appearance since the Bristol City game in November and it was not the most ideal situation to be put back into the first-team fold.
He told Footymad: "It wasn't the best game to make my comeback as the conditions were horrific and we got the worst possible start imaginable.
"We never raised our game to cope with the conditions like they did - both teams had to cope with the weather and they were better than us in that aspect."
The midfielder though remains upbeat and believes that if Wednesday work hard then they should make the post season.
He added: "We needed to win and there's a massive disappointment in the camp but we have to get our heads down and make sure we win the remaining games because we are not allowed to slip up any more otherwise it's going to cost us.
"You can't let the defeat dwell on your mind though and look forward - it was a terrible performance so we had to start back training on Monday to get on with the task at hand."