You have a choice:
1. Don't claim medical expenses, because you know you will be reimbursed, eventually. If for some reason, the reimbursement falls thru, you can file an amended 2019 return in the future.
2. Claim a medical deduction on your 2019 tax return. When you receive the reimbursement, in the future, you will have to claim a portion (the net deductible amount on your 2019 return) of it as misc. income.
You would have to do the math to see if one way was better than the other. That can be complicated. the medical deduction is only an itemized deduction subject to a 7.5% of AGI threshold.
