I need to extract expected future stock price from an option price. Could anyone please suggest me how I could do this?
If by "expected future stock price" you mean the stock's "forward price" for a given maturity (eg 1 year forward), F, then look at the price of all puts and all calls for this maturity, find the strike K such as the price of the put for this strike equals the price of the call for the same strike, C(K) = P(K), and K should be the forward stock price you are looking for, F = K. This comes from the Put-Call parity.
As Janthelme said the Put-Call Parity is the best approach. Nevertheless if you have enough Information you can also use the Interest Rate and the Dividend Yield to come up with an expected Future Stock level.
But remarkt the convexity of an option. Hence the todays premium is not equal the discounted value of E[S]-K.