Best thing to do is to call a team meeting and discuss the goals of a project. This would allow you to discuss the goals of the project without singling out any particular team member. The team can prioritize steps to solve the project together and the team can decide on what each particular team member should be doing. By setting goals together, all members of the team will have a clearer understanding of what each of them should be doing. This will allow the wayward team member to get back on track without singling them out.