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Laba went back to Argentina - signed with Estudiantes
https://www.mlssoccer.com/post/2018/01/27/matias-laba-officially-leaves-vancouver-whitecaps-fc-argentina-return

You have until the start of the season to become roster compliant, so the 4 DPs is fine, as long as they have 3 by season start time (as others have mentioned they will buy down one with TAM). ...