The 29-year-old recently launched his 'Common Goal' campaign, created to give professional players a chance to pledge a small part of their wage to football charities around the world.
Mata has now convinced others to join him, with Bayern Munich defender Mats Hummels, as well as 11 more unnamed players - seven men and four women - agreeing to the scheme.
Asked if any of his United teammates are willing to do likewise, Mata said: "They will. I'm almost ready to say who. We have more players coming but it is step by step."
When further probed if Mourinho was in on the charity initiative, he insisted that the Portuguese "will" pledge, adding: "The final idea would be for the whole professional industry commit, not just the footballers.
"Sometimes football can have a bad reputation but there are great people in football who are trying to help. I believe there are great values in football and, if this helps on that, then great.
"We are human beings and we react in different ways but everyone understands what we are trying to do. Everyone understands we are in a lucky position, we are privileged and many others are not so lucky. We are going to try and reach every footballer out there. I think it will get bigger in the next few weeks and months."
Mata, who recently entered the final 12 months of his United contract, is understood to earn £140,000 a week at Old Trafford.