The Knicks are awaiting insurance papers on Richardson, the New York Times reported. Richardson injured his back while playing for the Los Angeles Clippers, which reportedly was one reason they let him leave as a free agent.
Without the paperwork, the deal is unlikely to happen, the Times reported. If the trade is completed, the Knicks would also get a conditional first-round pick.
Thomas averaged 10.4 rebounds and 11.5 points in 37.5 minutes over 80 games.
Richardson averaged 14.9 points and 6.1 rebounds in 35.9 minutes over 78 games.