The veteran left tackle must sit out the next three games, however, because he and wide receiver Vincent Jackson were placed on the roster exempt list by general manager A.J. Smith on Aug. 20. McNeill will be eligible to play in Week 6 at St. Louis.
The two sides have the next few weeks to try to work out a long-term deal.
McNeill had been holding out in search of a long-term deal with the team.
Although the Chargers had been in talks to trade Jackson, it had not entertained offers for McNeill and San Diego had moved forward without him.
In McNeill's place, second-year player Brandyn Dombrowski has protected quarterback Philip Rivers' blindside as the Chargers have opened the season 1-1.
McNeill said on his Twitter account, "great to be back today.. GO BOLTS."
Adam Schefter is ESPN's NFL Insider. Information from The Associated Press was used in this report.
