Exhibit 99
Joint Filer Information
Each of the following joint filers has designated Onex Corporation as the “Designated Filer” for purposes of the attached Form 3:
| 1. | OMI PARTNERSHIP HOLDINGS LTD. 161 Bay Street P.O. Box 700 Toronto, ON, Canada, M5J 2S1 |
| 2. | ONEX CAPITAL SOLUTIONS GP, LLC 161 Bay Street P.O. Box 700 Toronto, ON, Canada, M5J 2S1 |
| 3. | ONEX CAPITAL SOLUTIONS GP, LP 161 Bay Street P.O. Box 700 Toronto, ON, Canada, M5J 2S1 |
| 4. | ONEX CAPITAL SOLUTIONS HOLDINGS, LP 161 Bay Street P.O. Box 700 Toronto, ON, Canada, M5J 2S1 |
| 5. | GERALD W. SCHWARTZ 161 Bay Street P.O. Box 700 Toronto, ON, Canada, M5J 2S1 |
Date of Event Requiring Statement: June 15, 2023
Issuer Name and Ticker or Trading Symbol: ATI PHYSICAL THERAPY, INC. [ ATIP ]
| Onex Corporation, by: /s/ Andrea Daly, Managing Director—General Counsel |
| OMI Partnership Holdings Ltd., by: /s/ Steve Gutman, Authorized Signatory |
| Onex Capital Solutions GP, LLC, by: /s/ Steve Gutman, General Counsel |
| Onex Capital Solutions GP, LP, by: /s/ Onex Capital Solutions GP, LLC, its general partner |
| Onex Capital Solutions Holdings, LP, by: /s/ Onex Capital Solutions GP, LP, its general partner and Onex Capital Solutions GP, LLC, its general partner |
| Gerald W. Schwartz, by: Andrea Daly, Attorney-in-fact |
Date: June 26, 2023
