It can be awkward to schedule a meeting with someone when the primary purpose of the meeting is providing critical feedback. The individual may or may not know that you have critical feedback to share, and if you are setting aside time outside of regular meetings to discuss an issue, you may feel compelled to give a reason for the meeting. There is one big mistake I've seen leaders make when attempting to handle this potentially awkward scenario - using the bait and switch approach. This is a definite "don't" in name of providing effective feedback!
What do I mean by the bait and switch approach? Telling the person when scheduling the meeting that you want to discuss one thing (e.g. a project update) but then sitting down to the meeting and saying "that's not really what I want to discuss today" and proceeding to blindside them with criticism.
While providing false pretense may make you feel better initially (by avoiding potential questions from the person about why you want to meet), that blindside isn't fair to the other person and it will damage their trust in your relationship - perhaps permanently.
If you need to schedule a meeting specifically for critical feedback, it's better to say something like "I'd like to process through how things went today, and discuss what went well and what could be done better next time. My schedule is tight today, let's put 20 minutes on the calendar tomorrow to touch base." This lets the person know you have feedback to provide, and gets time on the calendar, but also provides you with space to wait until the meeting to go into detail.
This is not to imply that every time you give feedback it has to be confined to a scheduled meeting - quite the contrary. Impromptu feedback can be exceptionally beneficial, but it's understandably not always feasible. If you have multiple office locations, a telecommuting workforce, etc. it can be necessary to schedule times for delivering feedback.
As you cultivate a feedback culture within your team, providing positive and critical feedback will be part of the natural rhythm of communication, and letting someone know you'd like to have a feedback meeting won't feel worrisome for you, or the other person.