The 32-year-old had a poor outing with the ball in the first Ashes Test at Edgbaston that England lost. In Australia's two innings, Moeen took just three wickets, conceding 172 runs. He was also dropped from the first team during the World Cup due to his poor batting form and has now been replaced by Jack Leach in the team ahead of the second Test.
"Mo is spending a little time away from the middle recharging his batteries and putting in some quality practice time which he feels he needs, and we completely respect that," Worcestershire coach Alex Gidman told the club's website on Tuesday.
"He has had an intense schedule of international cricket involving the World Cup and the start of the Ashes. Mo loves playing for Worcestershire and he gives a lift to everyone in the dressing room when he comes back and plays for us. We look forward to when he returns soon," Gidman said.
Australia have a good record at Lord's and will look to double their lead to strengthen their chances of winning a first Ashes on English soil since 2001.