Multiple teams are preparing to approach the San Francisco 49ers about their interest in trading for holdout guard Alex Boone, according to a league source.

Multiple teams are preparing to approach the 49ers about their interest in trading for guard Alex Boone, according to a source. AP Photo/Tom Gannam

Boone has held out since early in the offseason. The two sides are not close to a contract extension and Boone is believed to be prepared to stay away from the team until he gets a new deal. He has two seasons remaining on his contract that will pay him about a total of $4 million.

Boone signed a five-year deal in 2011 when he was a backup and the contract was essentially for backup money. He has developed into one of the better guards in the NFL.

Among the teams that could use a guard are the Buccaneers and Giants. Boone can also play tackle.

Trading Boone, a key part of the 49ers' offense, will likely be a last resort for the 49ers.

Joe Looney is working with the first unit in Boone's place. He struggled in the preseason opener at Baltimore on Thursday.