Act quickly. The poor performance is impacting on colleagues and customers.
Ascertain the facts. If possible observe for yourself the time-keeping and record keeping of your team member and contact the student.
Speak to the team member in private, away from the rest of the team, without interruption and allow plenty of time.
Explain the facts as you see them to the team member. Let him/her correct any errors of fact.
Ask the team member to explain why there has been this deterioration in performance.
What reasons might your team member put forward?