The Magpies reached the quarter-finals of the Europa League before they were knocked out by Benfica, but they have slipped down the top-flight table in recent weeks and are just six points clear of the relegation zone.
When asked if their exertions in Europe have affected his side, Pardew told reporters: "There's no doubt about that. This was our 50th game, which goes a little bit unnoticed.
"Fifty professional games and all the travelling involved as well ... that's tough. I think clubs will look at us as to the impact the competition can have; not only because of the extra games but the injuries that we've had on the back of them.
"It would be naive to argue that our League position would not be greater than it is without Europe."
Newcastle are 16th in the Premier League with four games to play this season.