Mikel Arteta has now sent a warning to his Arsenal players what they cannot afford to take their upcoming Champions League opponents Porto lightly. Arsenal will travel to Portugal to take on Porto in the first leg of their Champions League round of 16 tie on Wednesday. The Gunners will be heavy favourites heading into this clash with the Portuguese giants. However, the north London outfit cannot afford to show any complacency if they are to return to the Emirates Stadium with a positive first leg result in tow. Mikel Arteta may well take this opportunity to rotate his starting XI to some exten…