In a team, everyone should be pulling their weight. It isn't fair for a few members to carry the rest. If you're worried about getting your team mate into trouble, you might speak to them first to see if you can help them overcome any blockers. It could be something easily resolved.
If they're finding the work too challenging generally, or they're having issues in their personal life that are interfering with work, they need to speak to the supervisor.
In a team, everyone should be pulling their weight. It isn't fair for a few members to carry the rest. If you're worried about getting your team mate into trouble, you might speak to them first to see if you can help them overcome any blockers. It could be something easily resolved.
If they're finding the work too challenging generally, or they're having issues in their personal life that are interfering with work, they need to speak to the supervisor.
I think talking to him first is a good approach.