KANSAS CITY, Mo. -- Longtime NFL assistant coach Bill Muir followed through on his plans to retire, informing the Kansas City Chiefs on Wednesday that he wouldn't return for a 35th season in the league.

Muir joined the Chiefs in 2009 as offensive line coach under Todd Haley, and was elevated to offensive coordinator last season. But the Chiefs struggled with injuries and inconsistency, which resulted in the firing of Haley and the hiring of Romeo Crennel as head coach.

The 69-year-old Muir is considered one of the best offensive line coaches in football, though he wasn't expected to remain as the Chiefs' offensive coordinator if he stayed on the staff.

"It has been an honor to be a part of this great league for so long," Muir said in a statement issued by the Chiefs. "Over the years I've made a lot of great friends and worked with many talented players and coaches. This was a personal decision for me, the timing was right."

Muir played tackle for Susquehanna University, a small liberal arts college in central Pennsylvania, and got his start in coaching there in 1965.

He bounced through stops at Delaware Valley, Rhode Island, Idaho State and SMU before getting his break in professional football with Orlando of the short-lived Continental League.

His first job in the NFL was as a scout for Tampa Bay from 1978-81, and he returned to the Buccaneers more than two decades later, helping the franchise win its only Super Bowl.

In between, he spent time working with the offensive lines in Detroit and New England, and as defensive coordinator and offensive line coach in Indianapolis. Muir also spent seven seasons with the New York Jets as offensive line coach before returning to the Buccaneers.

"I have a tremendous amount of respect for Bill," Chiefs general manager Scott Pioli said. "I have worked with him for a long time and have witnessed him develop a number of very good football players. His contributions are very much appreciated and he will be missed."

Not by every fan in Kansas City, though.

Muir bore the brunt of criticism for the Chiefs' poor performance on offense last season, even though there were always questions about whether he was truly in charge. Haley's background on offense and tendency to micromanage led many to believe he was calling the shots.

It didn't help that Kansas City lost tight end Tony Moeaki and All-Pro running back Jamaal Charles to season-ending knee injuries in a span of three weeks at the start of the season.

Quarterback Matt Cassel joined them on IR with a hand injury sustained in Week 10.

The Chiefs still managed to play themselves into a position to defend their AFC West title despite struggling on offense. But their playoff hopes were dashed when they managed only 13 points in an overtime loss to Oakland in the penultimate game of the season.

Kansas City failed to score at least 20 points in its final nine games.

Crennel has been tight-lipped about Muir's potential replacement, though quarterbacks coach Jim Zorn and assistant head coach Maurice Carthon are considered internal candidates.

Crennel has indicated that it could be after the Super Bowl before he makes a decision.

"I'm excited for Bill as he moves into retirement," Crennel said. "I've known him for a long time and he is one of the finest coaches I've ever been around, and an even better person. Bill is a very good friend and I have a great deal of respect for the way he worked.

"It was a privilege to work alongside him."