How can I address a coworker's underperformance when my manager avoids the issue?

It makes sense that you feel stretched and frustrated. When one person’s missed deadlines pile onto everyone else for months, and your manager steers the conversation toward “support each other,” you are left carrying extra work while the real problem stays untouched. That is a workload and accountability issue, not a personal failing on your part, and it is reasonable to want a clearer path to fix it without turning the team against each other.

A constructive approach is to reframe the conversation around impact and capacity, not around labeling a coworker. Before you meet your manager, jot down a few concrete examples: which deadlines slipped, what work you or others absorbed, and how that affected your own deliverables or timelines. Stick to observed facts and outcomes rather than motives or character. Then ask for a short one-on-one, and open with a shared goal: you want the team’s commitments met and everyone’s load to be sustainable. For example, you might say that over the past several months certain handoffs have repeatedly landed late, which has required you to drop or delay your own work, and that you need help setting clear ownership and priorities so the pattern does not continue.

In that meeting, make a specific ask instead of only describing the problem. Useful requests include clarifying who owns which deliverables, whether deadlines can be adjusted when capacity is short, how the team should escalate when work is blocked, and whether the manager will check in with the person who is missing deadlines rather than redistributing the work informally. You can also propose a simple process change, such as a short weekly status check or written ownership of milestones, so follow-through does not depend on informal goodwill. If your manager again defaults to “support each other,” calmly restating the impact on your projects and asking what success looks like for you in the next few weeks can keep the discussion focused on outcomes.

If little changes after a clear, documented conversation, protect your own bandwidth: confirm priorities in writing, push back when new work is added without capacity, and note patterns in a factual way for future check-ins. Workplace dynamics vary by team and manager style, so there is no single script that always works, but staying calm, specific, and focused on workload and process usually reduces tension more than venting about a coworker does. That approach gives your manager something actionable to address while you keep your own professional standing intact.