The Portuguese boss hit out at Smalling and teammate Phil Jones as he urged them to "be brave" and step up their recoveries from knee and foot injuries respectively.
Smalling missed nine matches in April with the injury but he has no issues with the public pressure exerted on him by Mourinho to declare himself available.
"You can take positives from it in that the manager wants you out on that pitch," Smalling told Sky Sports News. "He wants you to represent him and be that fighter and warrior for him.
"Obviously with a knee injury there are certain protocols that need to happen. With the medical staff and with the coaches, we are pushing all the time. As players we don't want to be sitting on the touchline or watching the games in the directors' box. That is no fun. We have pushed as much as we can and I am glad to be back.
"We speak very closely with the manager and we have got a got a very good relationship. All throughout my injury we spoke about the process and when I would be back so it is good that the manager wants you because ultimately he has got that decision of whether you play or not."
Man United are currently in the middle of a personnel crisis, with six players sidelined through injury.