James, 29, is already a four-time MVP and two-time champion, but Thibodeau said his all-time ranking can't be properly evaluated until after his career is finished.
"Obviously, what he's done has been great," Thibodeau said Monday before the Bulls' game against the Cleveland Cavaliers. "I think it would be unfair to him to judge him now. I think when you're judging greatness, it's having the ability to judge it over a long period of time. Until he's done, we won't know ultimately, but he's right up there with the all-time best. When you look at it, to do it year after year, he doesn't miss many games, he's been very durable. He's a great competitor, and he makes his team win."
Thibodeau and the Bulls faced James twice in the postseason during his time with the Miami Heat, losing each time. Thibodeau was in charge of the Boston Celtics' defense for two playoff series victories against James during his first stint with the Cavaliers. He said James is capable of beating perfectly executed defenses.
"[There's] not many things he hasn't seen. Sometimes you could do it perfectly, and he still can hurt you. The idea is you want to make him work for what he gets, but you can't do it at the expense of leaving everyone else open.
The Cavaliers, who added James and Kevin Love during the offseason, are expected to compete with the Bulls for the top spot in the Eastern Conference this season. On Monday, James said the Bulls are a better team right now because they have more chemistry from playing together for several seasons.
The Bulls and Cavaliers play on Oct. 31 in Chicago.
- Paul Palladino