There is also to be another change of caddie for the former world number one in the run-up to next month's Ryder Cup after he lost Billy Foster to a knee injury in May.
Westwood missed the halfway cut in the USPGA Championship on Friday and so has now gone 59 majors without winning one. He will be almost 40 when the next one is played in April.
"Lee admits he needed to shake things up," manager Andrew "Chubby" Chandler said at Kiawah Island today.
"He'd lost his focus and his enthusiasm a bit because he wasn't getting the rewards for his long game.
"Parting company with Pete is because he's passing on advice to Lee, but he's not around to follow it through.
"Lee is very structured about going to the gym, but not about practising. Pete was here for two days with Graeme (McDowell) this week when Lee wanted to work with him, so it just wasn't working out.
"Lee's the sort who needs someone standing over him, making him hit chip after chip and telling him what he's doing wrong.
"It's not like he's got the yips or anything - he just needs to improve his technique.
"He's not going to have a long game coach for the foreseeable future - there's nothing wrong with that part of his game, as you could see from the fact that he topped the greens in regulation stats here for the first two rounds.
"When you miss the cut after that it gets even more frustrating and that probably brought matters to a head.
"It does start to get you down when you keep walking off feeling disappointed and frustrated, so we're going to put a few things in place - including a new short-game coach.
"I won't say who it is, but it will become public next week because he'll be working with Lee for a few days at The Barclays (first of the FedEx Cup play-offs in America).
"All I'll say is that it's not one of the usual suspects - it's someone a bit different. It's an interesting choice.
"Lee needs to try something different with his chipping and putting - he's never been the greatest chipper, but his putting also needs work. He knows that."
Westwood went into the final major of the season ranked 190th out of 193rd on the PGA Tour in getting up and down from off the green.
On the caddie front, he has been using Mike Waite as his caddie since the end of May, but has now hired Mike Kerr, who is available following Spaniard Alvaro Quiros's decision to take a break after falling down the Ryder Cup standings and out of the reckoning for a debut.
At the end of this year the Worksop golfer is moving home to Florida and Chandler believes that may have also played a part in the changes.
"Being over here full-time would have made it difficult for Lee to work with Pete. He's already seen that from playing more on the US Tour this year."
It is not the first time he and Cowen have parted. It happened for a while during the worst slump of his career more than a decade ago - one that saw him nosedive from fourth in the world to outside the top 250.
Ryder Cup captain Jose Maria Olazabal will be desperately hoping that Westwood rediscovers form. Europe defend the trophy in Chicago in less than seven weeks.