"He was frail, you might say, but something seemed to happen over the weekend, and he came into rehearsal on Tuesday and something really extraordinary seemed to happen. He came on stage at 9 in the evening and we all looked at each other and it was something that said he really had it," Woodroffe said.
Woodroffe said the artist was performing extremely well.
"Suddenly, he was performing as one had remembered him in the past, and he was singing. A lot of the times the director and engineers will say, 'Hold your voice. Don't sing out,' and it was almost like he couldn't stop himself," Woodroffe said.
But by the end of the run-through, Woodroffe said workers believed Jackson could pull of the hectic concert schedule.
"We all had a view as to whether he would be able to survive these 50 shows and whether he could have. I couldn't tell you, but I can certainly tell you he would have made it to the start of the race if you know what I mean," he said. "Whatever the view of Michael Jackson is, there's this sense that he would have done it and that was exciting.'
The King of Pop has struggled with his health since 1984 when he became addicted to painkillers after receiving severe burns filming a Pepsi commercial. The pop star's hair caught fire, leaving Jackson in excruciating pain.
A former family lawyer told "GMA" he knew Jackson had a drug problem.
"I spoke to family members. I said to them, If this situation arises where Michael perishes because of medications, and my words were, 'If he one day wakes up and he's dead because of these medications, I will not hold my tongue. I will speak out and I will speak out loud,'" said former family attorney Brian Oxman.
In 1995, Jackson collapsed while rehearsing for a television special. His doctors said he fainted because of an abnormal heart rhythm caused by dehydration.
Jackson had an anxiety attack at a copyright lawsuit court appearance and was treated with intravenous fluids and tranquillizers in 2003.