According to America's InTouch magazine, the sportsman has been shopping for engagement rings at an upmarket New York jeweller.
Diaz proved her commitment to Alex and his daughters by recently moving to Miami to be closer to them.
Although she may now be considering marriage, the 38-year-old beauty has previously claimed she is in no rush to settle down.
When quizzed about her thoughts on marriage and children, Cameron - who has dated a string of Hollywood hunks, including Justin Timberlake, Jared Leto and Matt Dillon - said: "What about it? If I say, 'This is how I'm going to live my life,' I am closing myself off to all these other possibilities. I'm the kind of girl who likes to be open to every possibility, who is open to all my options."
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