Derek Fisher says Carmelo Anthony needs to be focused on family ... not basketball ... and promises he'll reach out to his former player and help him cope with the separation from his superstar wife, La La.

Derek coached Melo on the Knicks a few years back -- and when we got him out in Calabasas with his GF, Gloria Govan, we had to ask if he'd he heard the news about Melo's marriage.

Interesting question for Fisher (Govan LITERALLY sips tea when we ask) ... but he goes full-on friend, saying Anthony should tune out everything except his family. He also promises to call Melo to offer his support.

Nothing to see here, Matt Barnes.