Thank you for your query. I will answer your query and give a few more points of advice.

Affiliation

First, you should check the guidelines for the journal. Sometimes, journals have specific instructions when somebody is no longer part of an institution. In that case, those instructions take precedent over my advice.

If no such guidelines exist, you can indicate their status as an affiliation. Let’s say you are Jane Smith and the professor is John Doe, your Author and Affiliation sections could look like this:

Jane Smith¹, John Doe²

¹Department of Examples, University of Place

²Retired Professor, formerly of Department of Examples, University of Place

They may also have a symbol used to show that somebody is a former member of an institution, such as an octothorpe (#), dagger (†), or section sign (§), or they may let you use these symbols freely for any notes you have. In such cases, it could look like this.

Jane Smith¹, John Doe^1,#

¹Department of Examples, University of Place

^#Retired Professor

Author Contributions

You should make their role clear in the Author Contributions section if possible. If it is a free text section, you can say something like:

John Doe was involved in the conception, planning, and data acquisition of this study but retired before its conclusion.

If the journal follows guidelines like CRediT Taxonomy, you can add any keywords that fit their role. Make sure that you don’t add any points that occurred after they retired; e.g., they probably aren’t helping you with writing – review & editing.

Declarations and covering letter

Most journals want you to say that all authors have read and approved the final version of the manuscript either in the covering letter, back matter, or both.

You should get in touch with the retired professor and get their consent so you can accurately say that all authors have read and approved the final version. If this isn’t possible, then you can say something like this:

We declare that all current authors have read and approved the final version of the manuscript. Please note that Professor John Doe, who contributed significantly to this work, has since retired and is currently unavailable for communication. However, all other authors have reviewed and approved the final version of the manuscript.

I wish you all the best for your submission!