Former Swansea and Leeds United defender Fede Bessone has been training with Millwall.
The 30-year-old left-back, who spent two separate spells with the Swans, recently turned down a three-year contract extension at Major League Soccer side Sporting Kansas City.
Bessone signed for the MLS club in September 2013 but ended up leaving without making a first-team appearance.
The Argentinian, who once had a loan spell with Charlton from Leeds, told Sky Sports: "The club (Sporting KC) offered me a new three-year deal.
"We were close. It was a difficult decision for me not to stay there, but it's great to be in London again."
Bessone also counts Swindon and Oldham amongst his former clubs.