My coworker keeps promising “we can have it by Friday” before asking me

In a client call yesterday, my coworker said, “We can have the revised analysis to you by Friday.”

The “we” was me.

He manages the client relationship. I build the reports. He had not asked how long the revision would take, and he did not know that I was already finishing two month-end deliverables. After the call, he messaged, “Hope Friday works!” with a smiley face.

This is the fourth time in six weeks that he has volunteered a deadline on behalf of both of us. Each promise sounds small in the meeting. Add one chart. Recut the data by region. Turn the notes into a one-page summary. Then I open the request and find missing inputs, conflicting definitions, or three rounds of review hidden inside the word “revise.”

The first two times, I made the deadline. That was probably a mistake. He learned that his estimates were accurate because I absorbed the difference after the call.

The third time, I told him the date was not realistic. He replied that changing it would make us look disorganized. I said the disorganization had already happened when he promised work without checking. We ended up delivering a thinner version on time, and he thanked me for being flexible.

Yesterday I did something different. Before the call ended, I said, “I need to check the existing queue before we confirm Friday. I can send timing by 2 p.m.” There was an awkward pause. The client said that was fine. My coworker later told me I had undermined him in front of the client.

I do not enjoy correcting a colleague publicly. I also do not see how a private conversation can repair a deadline after it has already been offered as a fact. He thinks speed reassures clients. I think a deadline nobody checked is not reassurance; it is a gamble placed with someone else's time.

Our manager has told us to work it out between ourselves. She suggested that I give him standard turnaround times. I can do that for familiar requests, but the difficult work is difficult precisely because the scope is unclear. A menu will not stop him from choosing the shortest line.

I want a simple rule: he can promise the date only when it falls inside an agreed service window and the request is complete. Everything else gets confirmed after I assess it. He says that sounds bureaucratic.

Would you keep correcting the deadline in the room, insist on a pre-call review, or take this back to the manager with examples? How do you protect delivery credibility when a coworker believes credibility means never making the client wait for an answer?