He's scheduled to visit the San Diego Chargers on Tuesday, a visit that got scheduled tonight.
No deal has developed at this stage, though, with the source saying: "Nothing more than [a] visit right now."
The Ravens haven't made an offer for McKinnie to return, but haven't entirely closed the door on potentially bringing him back.
McKinnie, 33, is an unrestricted free agent who started every game in the playoffs after being replaced at left tackle during the regular season by Michael Oher.
The 6-foot-8, 354-pound New Jersey native has been working out regularly in South Florida. McKinnie has battled conditioning and weight issues in the past.
McKinnie was contacted by the Chicago Bears when free agency started, but they quickly reached a deal with former New Orleans Saints and Towson offensive tackle Jermon Bushrod as their new left tackle.
During the playoffs, McKinnie excelled and drew praise from Ravens coach John Harbaugh for stonewalling several top pass rushers during victories over the Indianapolis Colts, Denver Broncos, New England Patriots and the San Francisco 49ers to win the Vince Lombardi trophy.