We have a daily online "scrum" during which I repeatedly asked him how it's going, and if there were any blockers. He replied, "I'm working on it". I knew it was a significant task so I didn't expect it to be done quickly, but I did expect far more progress than what was delivered.
Perhaps what you need to do is simply expand the scope of your standup to include a 30-second description of what was done yesterday, beyond merely reporting blockers.
If that turns out to be "I was not able to work on this project yesterday" at least you have visibility into the situation.
If the summaries are a lot of excuses, at least the picture becomes clear.
If the person refuses to communicate, don't settle for something meaningless like "I'm working on it", push until you get a meaningful answer.
Hopefully the summaries will be more meaningful, ie "spent most of the day banging my head against the wall over issue X but finally solved it by applying Y so am now able to move on to step Z"
It's not worth arguing about if this does or does not fit some other organization's idea of what a standup is for; process needs to fit the needs of your project, and if it presently does not, then it needs to be modified until it does.
If all you ever get from this process is excuses for making little effort day after day, then you may want to start making it obvious to the person how this is sounding. You could try to get a client representative to participate in the meetings. Better yet, you could take notes and send around a daily and weekly summary of these self reports, addressed to the client and CC'd to the team.
Hopefully seeing his non-performance side by side with the progress (or at least effort) of the rest of the team will start to activate his own internal criticism - if you can do that, it will be a lot more effective than pushing for the outside.
And if it doesn't work, you have a very clear record of under-effort to discuss in more formalized meetings.
Conversely, if you get reports of effort that never lead to success, then you have the basis to have an engineering meeting on the details of the frustrating technical problem itself.