McDaniels declined on Thursday to comment to reporters on Kaepernick's workout with the Raiders, stating that he does not discuss players who are not currently on roster.
"Just by standard procedure, we will only talk about the people that are on our team," McDaniels said. "[General manager] Dave [Ziegler] and his staff have worked out tons of guys this spring, and we really don't make comments about the evaluations that we've made; or what they look like, what they didn't look like.
"They're kind of private for us as we look at things to try to make decisions to make the team better."
NFL Network Insider Ian Rapoport reported Thursday that all indications are that Kaepernick's workout went well and that the quarterback impressed those in attendance.
The workout was Kaepernick's first with an NFL team since he parted ways with the San Francisco 49ers following the 2016 season. Kaepernick had a free-agent visit with the Seattle Seahawks in May of 2017, and recently threw in front of NFL scouts during halftime of the University of Michigan's spring game on April 2.
Kaepernick has not played in the NFL since the 2016 season, during which he peacefully protested social injustice and police brutality by kneeling during the national anthem prior to games.
"If there's an opportunity to improve the team, we've said it from Day 1 that we would look at every opportunity," McDaniels said when asked about Kaepernick's workout. "He's not the first player that we've looked at, and not the last one. There's going to be a lot of people that are going to come in and out of this building. ... The evaluations we make are private for us, and if we make a decision to add someone to the team then we'll do it."
Derek Carr is entrenched as the Raiders' starting quarterback after signing a three-year extension this offseason. Nick Mullens, Jarrett Stidham and rookie Chase Garbers are the other quarterbacks on Las Vegas' roster.
"There's nothing more important than that position," McDaniels said. "So when people say you know you've got it established, we certainly do. The next guy in line, you don't really talk about him until he's the most important guy in your organization when the starter gets hurt. I know there's a lot of us on this staff that have lived through some of those injuries; I certainly have experience with that. It's one of the toughest positions, if not the toughest position to play in all of sports.
"To try to constantly shuffle through and make sure you're doing the best you can to provide competition in that room and to have guys in there that can learn and play and produce in your system with the group that we have is really an important part of any football team, and we're encouraging the competition right now."