According to Barry Jackson of the Miami Herald, McClain's "visit to the Dolphins ended without a contract. But it remains a strong possibility down the road. Sides will keep in touch."
McClain, 29, appeared in 12 games for Washington last season, registering 20 tackles, two sacks and a fumble recovery. Pro Football Focus gave him a grade of just 41.8, 120th among interior defensive linemen.
McClain signed a four-year, $21 million deal with Washington last offseason but was cut just one year into that contract.
He's also had stints with the Carolina Panthers, Houston Texans and Dallas Cowboys in his career.
In San Francisco, McClain would compete for playing time with a fairly deep crew of interior defensive linemen, headlined by DeForest Buckner and also featuring Earl Mitchell, D.J. Jones and Sheldon Day. McClain may not start, with Buckner and Mitchell currently penciled into that role, but he would be another nice depth piece for the squad.