Use gzip to compress the files in a directory except for already existing .gz files

I have a directory of logs that I would like to set up a job to compress using gzip . The issue is I don't want to recompress the logs I've already compressed. I tried using ls | grep -v gz | gzip, but that doesn't seem to work. Is there a way to do this? Basically I want to gzip every file in the directory that does not end in .gz.