I am looking for a word (or phrase if word is not possible) that is the opposite of associate. The context being when you have a collection of people and they are all part of a respective groups, clubs etc because that is expected but then there is one new person who is essentially independent. Once a person is already in a group/club then it is easier to get accepted into another one because their reputation is based on the group/club they were in before. But when a person is independent the collection of people in their respective groups/clubs etc are skeptical about accepting them because they are by themselves and therefore do not have a reputation established yet, similar to when you are applying for the very first job and the employer is skeptical about whether to take a risk and hire you even though you don't have a proven track record.
"Independent" is quite close, but I am looking for something less formal like "outsider" that you could use to describe a person compared to several groups of friends for example. I am also not thinking derogatory like "loner", but more like a "lone wolf".
"I don't know if we can accept him/her, they are ________."
"We haven't accepted a _______ for a long time, the rules are they have to be part of another group for at least 2 years first."