Simms suffered a high ankle sprain when Seahawks pass rusher Nick Reed fell on his left ankle during the third quarter of Saturday's 27-13 loss at Seattle, and the Broncos have not said how long Simms is expected to be sidelined.
"Under our current situation, with only two quarterbacks that can come out and practice, it felt like it was better for us to do that," add Martin, coach Josh McDaniels said. "He's got good size, a decent arm. He's a smart kid. He's a guy that we felt like could come in and help us compete right now and see what happens."
Martin joined the Broncos in time to take part in Wednesday's practice, though he went through the workout in a numberless orange quarterback's jersey.
"Hopefully, the equipment guys will hook me up tomorrow," Martin said with a smile.
The Broncos are the fourth NFL team for Martin, who was released earlier this month by the Kansas City Chiefs after splitting time last season between their active roster and practice squad. Martin came into the league in 2006 as a fifth-round draft choice of the Green Bay Packers. He also spent two years with the Tennessee Titans.
"When you're a guy like me, you just want an opportunity and that's what I've got here," Martin said. "Hopefully, I can come in and show them a little bit of what I can do and make myself stick."
Martin said he's taking a crash course on the Broncos' offensive scheme in hopes of being able to function in the system as quickly as possible. It was uncertain whether he would see any playing time in Sunday night's exhibition against Chicago.
NOTES: To make room on the roster for Martin, the Broncos waived running back Marcus Thigpen. ... Running back Lamont Jordan, apparently banged up in the Seattle game, missed a second consecutive day of practice. ... Lost in the hoopla over Bears' quarterback Jay Cutler's return to Denver is Orton's first opportunity to play against his old team. Said Orton, "I look forward to every game that we play, and this is certainly one more chance to face a good defense. They've got a great defense over there and they've been that way for years."