Crabtree is expected to arrive in Oakland Wednesday, take a physical and then make the deal official, NFL.com reported. The deal is reportedly for one year, according to the report.
Crabtree, the No. 10 pick of the 2009 draft, played his first five seasons with the San Francisco 49ers. In 2014, Crabtree played in all 16 regular season games but only caught 68 passes for 698 yards, his fewest catches and yards in a full season since 2010.
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Crabtree's best year came in 2012, when he had 1,105 yards on 85 receptions. He missed most of the 2013 season due to a torn Achilles.
Crabtree will join James Jones, Andre Holmes, Kenbrell Thompkins and Brice Butler as receivers in Oakland.
For the 49ers, Crabtree joins Patrick Willis and former coach Jim Harbaugh as departures from the team that made three straight NFC championship games from 2011-2013. Linebacker Chris Borland also retired this offseason.