In an unusual act of cooperation between rival networks, Craig Sager, TNT’s vividly attired N.B.A. sideline reporter, will be on ABC’s broadcast for Game 6 of the N.B.A. finals from Cleveland on Thursday night. He is scheduled to cover the Golden State Warriors.

Sager has never worked the sideline for an N.B.A. finals because TNT’s rights do not go past the conference finals. The opportunity to work for ESPN, which produces the games for ABC, comes as Sager continues to be treated for acute myeloid leukemia, which recently returned after being in remission. Admired for his idiosyncratic work at Turner Sports, he has become an inspiring presence around the league and will receive the Jimmy V Perseverance Award next month on the annual ESPYs awards show, which will be shown on ABC.

“I feel good,” he said in a telephone interview. “My energy is there. I’m able to do my job with no complications.”

ESPN began its internal discussions about inviting Sager to work on the finals about six weeks ago.

Referring to ESPN/ABC’s lead announcing team, Tim Corrigan, ESPN’s senior coordinating producer for the N.B.A., said: “My first conversation was with Jeff Van Gundy, and then with Mike Breen, Doris Burke and Mark Jackson. Everybody said, ‘We’ve got to do that.’”