The Blues manager has deployed Spanish right back Cesar Azpilicueta on the left for two matches and been pleased with the results.
The England left back watched the last two Blues games - a 3-0 win over Schalke in the Champions League and Saturday's 2-2 draw with West Brom - from the bench as an unused substitute after the manager opted to give the Spaniard the nod.
Mourinho feels that his decision to play Azpilicueta - a right back by trade - ahead of Cole has paid off but told the England international that he will be welcomed back into the starting XI if he shows more "fight."
"I decided for Azpilicueta to play against Schalke and he was fantastic," the Portuguese told the media. "On Saturday, he was very good again. Ashley is a top professional, he is a fighter. He has to work hard, to fight hard because the place [in the side] is his place. Of course, it is not Azpilicueta's best position and it is not a position where Ashley can think that he is in trouble now. No, he has to just work, fight and the position is there waiting for him, no problem."