alphanumeric counter

I'm probably making this harder than it needs to be, but here goes. I need to automatically populate a column with an alphanumeric MFR0001 to MFR9999 and am currently using the formula below to add 1 to the start point (A1)...

A1=MFR0001
Formula in A2 =LEFT(C1,3)&(RIGHT(C1,4)+1)

This works perfectly if I start at MFR1000, but breaks and drops the 000 if I use it on the number I need to start with (MFR0001).

Can anyone give a guy a hand on this?