Reports first emerged in the Pakistan media and ESPNcricinfo understands that a formal announcement is due to be made within the next day.
Rehman, 32, played four Championship matches for Somerset and took 27 wickets, which included 9 for 65 against Worcestershire, and flew straight back from Pakistan’s one-day series against Australia in the UAE to play the match against Sussex.
He was expected to join a Sialkot Stallion conditioning camp this week at the National Cricket Academy ahead of the Champions League Twenty20 but did not turn up to join the squad. Sialkot are set to fly to South Africa on October 7 to play a qualifying round of the tournament starting on October 9 in Johannesburg.
Rehman has established himself as key player over the past year and caused England plenty of problems during the Test series in UAE, where he claimed 19 wickets in three matches. Overall he has 81 wickets in 17 Tests at 28.40 apiece.