MANCHESTER, TENN. — It’s Jack Johnson to the rescue at Bonnaroo.

Johnson has agreed to take the Saturday night headlining slot at the Bonnaroo Music and Arts Festival after Mumford & Sons were forced to cancel due to bassist Ted Dwane’s illness.

Festival officials announced the move Friday morning. The “Upside Down” singer last headlined at Bonnaroo in 2008.

“I called my band and asked if they were up for it,” Johnson said in a statement. “Long story short — they are headed this way. I’ve got a lot of lyrics and chords to relearn by Saturday night. I was here to play the first Bonnaroo, and it is a very special festival to my band. We are excited to hit the stage again. Get well Ted!”

Mumford & Sons’ decision comes after Dwane received treatment this week for a blood clot on his brain. The band postponed three shows in Dallas and Woodlands, Texas, and New Orleans after the blood clot was discovered but hoped to play Bonnaroo on Saturday night.

Dwane has been discharged from the hospital and is recovering from the procedure but is not yet ready to play. Rather than perform with a replacement, the London-based, Grammy-award-winning folk rock band decided to pull out. The band also canceled appearances at the Telluride Festival in Colorado and a performance in Bonner, Kan., ending their summer tour early.

“The surgery went well, and the excellent medical team helping him are very pleased with his progress,” a band statement said. “He has been nothing short of heroic in how he has handled the whole ordeal, and now it has been medically proved that he does indeed have a brain.”

It was a case of right place, right time for Johnson.

The 38-year-old Hawaiian folk-rock singer was in town to play with friends ALO on Thursday night. He also was already scheduled to be in Manchester this weekend to perform a small secret show for reporters and participate in a question-and-answer session to promote his new album, “From Here To Now To You,” which is due out in September.