A knee injury has forced Rory MacDonald out of next month's UFC 123 event, and Brian Foster has agreed to step in as a replacement and fight fellow welterweight Matt Brown.

Sources close to the show confirmed the switch, though UFC officials have not formally announced it. Foster vs. Brown is expected to keep its spot on the night's Spike TV "UFC Prelims" broadcast.

Brian Foster (14-5)
Win Forrest Petz - TKO (Punches) UFC FN 22
Loss Chris Lytle - Submission (Kneebar) UFC 110
Win Brock Larson - Submission (Punches) UFC 106

Matt "The Immortal" Brown (11-9)
Loss Chris Lytle - Submission (Straight Armbar) UFC 116
Loss Ricardo Almeida - Submission (Rear-Naked Choke) UFC 111
Win James Wilks - TKO (Punches) UFC 105

Main card:
Quinton "Rampage" Jackson (30-8) +260 vs. Lyoto Machida (16-1) -340
Matt Hughes (45-7) +120 vs. B.J. Penn (15-7-1) -135
Gerald Harris (17-2) vs. Maiquel Falcao (25-3)
Phil Davis (7-0) -650 vs. Tim Boetsch (12-3) +450
George Sotiropoulos (13-2) vs. Joe Lauzon (18-5)

On Spike:
Aaron Simpson (7-1) +155 vs. Mark Munoz (8-2) -185
Brian Foster (14-5) vs. Matt Brown (11-9)

Preliminary card:
Karo Parisyan (19-5) vs. Dennis Hallman (45-13-2)
Darren Elkins (12-2) vs. Edson Barboza (6-0)
Paul Kelly (10-3) vs. Gabe Ruediger (17-6)
Tyson Griffin (14-4) vs. Nik Lentz (21-3-2)