I am assuming that you generated a transfer function using idtf command as shown below.
num = [1 4];
den = [1 20 5];
sys = idtf(num,den);
The following command can be used to convert idtf data format to tf data format.
[num, den] = tfdata(sys)
As the output is obtained in cell array format, use num{1} to get the numerator coefficients and use den{1} to get the denominator coefficients.
Refer to the below link for more information.
