What is the name of your state? What is the name of your state? Indiana
Your friend will want an attorney to assist in clearing the warrant, before your friend is arrested.
If arrested and in jail, it can be more difficult for him to reach an attorney who can respond quickly.
There is always a chance that the probation violation will not result in a revocation of probation but the fact that a warrant had to be issued indicates that this is not a minor matter.
We have as a member of this forum who is a probation officer from Indiana. Perhaps "Indiana Filer" will stop by to offer some additional advice.
Good luck.