I don't know where your problem is.
No MCU understands current and expects voltage at the A/D converter.
Here is an amplifier circuit with a total amplification of up to 1,104:1.
100µV voltage drop at the primary winding will give you enough voltage at the amplifier output to evaluate the motor condition. Using a toroidal core of 20 to 40 windings requires just 2 to 4 on the secondary side.
Also, I guess it's not a biggy putting a few windings of wire into a toroidal core, where you don't have to observe not to twist the wire to avoid breaking of the enamel. (Use 0.75 square mm household stranded cable for the secondary winding)
Please note the circuit is made to amplify negative voltage. Turn around the rectifier diodes to gain positive voltage.
If the output voltage is too low increase R4 value. R7 just reduces high spike charging pulses.
The time constant of R5, R6, R7 and C3 is 50ms.
The circuit is cheap to build and will do the required job properly.
Boncuk