The 30-year-old defender received the necessary work permit allowing him to sign for Millwall and manager Kenny Jackett wasted no time in offering him a deal, if only to cast his eye over the player for another month.
"The situation with Brent is similar to that with Bayo Akinfenwa," Jackett told the club's official website. "He hasn't been with a club so we are able to sign him even outside the window for loan signings.
"It's an opportunity to show us what he can do over the next few weeks and then we'll see where we go from there.
"Brent won't be involved at Leyton Orient but will play for the reserves against Charlton at Ebbsfleet on Wednesday night."