Stem cell pioneer Hwang Woo-suk on Monday failed again to show up at his Seoul National University lab.

His research team said he did not go to the lab for the fourth straight day after going into seclusion to rest following his news conference Thursday.

Hwang had arrived at the lab at 6 a.m. daily without fail over the past three years, often staying there late to conduct his research.

In an interview with KBS Monday morning, team member Lee Byung-chun said Hwang is apparently more upset than expected, adding Hwang did not mention a possible return date.

Lee warned that Hwang's continued absence will seriously affect the team's work, especially stem cell experiments, and that he hopes for an early return to minimize potential disruption of the research process.