Gleeson, the fast bowler who was an England reserve for last summer's ODI series against Ireland, has struggled with injuries over the last two years, making only two appearances for Lancashire since September 2019 due to a stress fracture in his back. He bowled a single over in the opening game of the T20 Blast season before suffering further pain and has been ruled out of the month-long competition.
Overton, meanwhile, suffered a calf injury during Surrey's County Championship fixture against his old club Somerset last week, which limited his involvement in the game to four overs. He had missed out on selection in the Hundred's initial draft in October 2019 but was signed on a £48,000 contract in February this year after reinventing himself as a T20 finisher in the Blast.
Both players were due to play for Manchester Originals, who have recruited Dan Douthwaite and Calvin Harrison as last-minute replacements. Douthwaite, the Glamorgan allrounder, was the club's leading wicket-taker in the Blast this year with 15, and scored 203 runs at a strike rate of 153.78 in a finishing role similar to Overton's.
For Harrison, the legspinning allrounder, selection in the Hundred is the latest marker in a rapid rise this summer. He had played only two professional games before 2021, both for Hampshire in last season's T20 Blast, and spent the winter completing a psychology degree at Oxford Brookes University.
He scored 121 and took three wickets against Nottinghamshire in a pre-season game for Oxford UCCE, earning himself a trial for their second XI and then a three-month contract, and has now signed a two-year extension after taking 18 Blast wickets while conceding 6.78 runs per over. He will be the Originals' third-choice spinner after Matt Parkinson and Tom Hartley but could be picked if they replicate Lancashire's spin-heavy strategy in home games at Emirates Old Trafford.
The ECB are expected to confirm the signings shortly.
Matt Roller is an assistant editor at ESPNcricinfo. @mroller98