"I touched the ball first but the referee has a fraction of a second and my leg was high and I touched Campbell as well," Sky Sports News quotes him as saying.
"It wasn't my intention to kick him, but once the referee has made that decision there's nothing I can do. He has to make those decisions so I can't complain.
"I was the last man because everyone was forward so I had come up to defend a big area. It was a shame, but it didn't make a difference in the end."
Swansea continue their Europa League campaign on Thursday when they make the trip to Russia to face Kuban Krasnodar.