Siemian showed mobility and zip at practice Friday while again splitting snaps with Paxton Lynch.
Kubiak said there's always a risk of re-injury for any player, but the Broncos would feel good about putting Siemian back on the field with an orthotic and tape, "but the bottom line: can you do what you need to do to play? And he's shown the last couple of days that he's been doing that."
"The hatred by some against people of color is one of the reasons we are where we're at in the world today, and they wonder why we feel the way we do and take the stances that we take," Marshall wrote. "I received this letter at work."
Asked what the Broncos security personnel department was doing in light of the letter, Kubiak said: "I was not much aware of that until this morning, but I know that our organization is on top of it. That's all I can tell you."

After Sunday, their opponents are a combined 30-8.
Kubiak said he'll make his decision Saturday, but it was apparent the start is Simian's if his health allows.
"Yeah,Cheap Shoes China Wholesale, just (see) how he's coming in. He came in today, he felt good. We pushed him a little bit harder today," Kubiak said. "Heck, I still see him out there doing some extra. So, a bunch of good signs. But we'll see how he's doing tomorrow."
DeMarcus Ware said that was just the latest piece of evidence that Miller should be the league's hands-down Defensive Player of the Year,Steelers Color Rush Jersey.
Linebacker Brandon Marshall (hamstring) was ruled out for Sunday,Andre Smith Jersey. Corey Nelson will start in his place and outside linebacker Dekoda Watson will move inside to help defend against Titans tight end Delanie Walker.
"Everybody is hurt, it's late in the season," wide receiver Emmanuel Sanders said. "We have four games left. You give me a player out there on the field that's not dealing with some type of injury or some type of nagging pain, then it's his first time playing. Everybody is hurt."
Sanders praised Siemian's toughness: "He's been fighting through injuries and that's what it's going to take for us to get to the championship,Cheap NFL Jerseys Store."
Von Miller, the NFL sacks leader with 13 1-2, said he might play Sunday with a brace on his left elbow like he did at practice this week.
Siemian may not be 100 percent, but he's shown this week that he's healthy enough to move around the pocket and step into his throws.
Siemian was injured in Denver's overtime loss to Kansas City on Nov. 27 and sat out last week's game at Jacksonville, where Lynch picked up his first NFL win despite completing just 12 of 24 passes for 104 yards and no touchdowns.
The Broncos face a daunting task in trying to return to the playoffs a year after winning it all. All four remaining opponents are division leaders or co-leaders.
Miller injured the elbow at Jacksonville, where he was constantly double-team and even chipped by a third player on just about every pass play but still managed to force two turnovers that led to 10 points.
Kubiak said running back Justin Forsett is ready to jump in and help Denver's depleted backfield after being claimed off waivers this week.
"He's ready to go. I will play him. Will it be half the time? Will it be less than (Devontae Booker)? More than Book? I don't know, we'll see how the game goes," Kubiak said.
"If you don't have two or three guys on him, you're going to have a problem," Ware said. "He finds ways to win games. He finds ways to make big plays all of the time."
Marshall posted on Facebook and Twitter a racist,Adidas NMD Shoes Cheap, profanity-laced letter he received criticizing him for kneeling during the national anthem earlier this season to protest racial injustice .
ENGLEWOOD, Colo. (AP) — Trevor Siemian is on track to return to the Denver Broncos' starting lineup Sunday at Tennessee barring a setback.
"I hate that Kubes had to put that on the injury report, but that's what you have to do. I'm ready to go. It's really a non-factor for me," Miller said.
Coach Gary Kubiak officially listed Siemian as 50-50 but indicated that if he shows up Saturday like he did Friday — without pain or soreness and able to move around — he'll be back under center when the Broncos (8-4) face the Titans (6-6).