mbedTLS RSA encryption without entropy

I am trying to use mbedtls library to encrypt a message with RSA. I am using a Arm Cortex M3, so it does not have a TRNG. I have changed to config file to allow the usage of the library without entropy sources. My question is, can I still encrypt a message using RSA without entropy sources? And if so, how can I do it using the mbedtls_pk_encrypt function?
I am sorry if this question sounds dumb, but I am new on encryption.
Thanks in advance!

Hi @rujma
For RSA encryption, you must use an RNG.
Have you considered using the NV seed feature?
Mbed TLS Support