The Europa League holders have already had two big-money offers for the unsettled England international rejected and Mourinho hinted after Sunday's 2-0 win over Hull City that he would eventually make a third attempt to sign Rooney.
"We have Plans B and C," the Portuguese told a news conference on the eve of Wednesday's home game against Aston Villa in the Premier League.
"Don't ask me names because it's difficult to speak about players from other clubs. We have the conditions to try to improve our team by bringing in one more player and we are going to try that till the end."
The club's player of the year for the last two seasons has been troubled by a thigh injury but said he was now ready to return.
"I didn't train for a few days but I came back, worked with the physios and on Thursday last week I trained with the first team, not at 100 percent but trying to get to my best," Mata said.
"Now I feel better and I am looking forward to playing and starting my season."
Mata was an unused substitute against Hull and said he was impressed with Chelsea's performance, especially in the first half when they scored twice and missed a penalty.
"It was a very good start," the Spaniard added. "The first 30 minutes were amazing.
"The team pushed, pressed and recovered the ball very high (up the pitch) and scored two goals. It could have been even more and we played well."
Eden Hazard was one of the standout performers in the opening 45 minutes against Hull but Mourinho is demanding more from the talented young Belgium playmaker.
"I know what I want from him - I want more responsibility and I want more ambition because when you are a normal player you have to be happy when you perform okay," the Chelsea manager said.
"When you have top talent (like Hazard) you cannot waste that talent so I want to give him that ambition to be better and better and to express himself on the pitch match after match, not be up and down."
Mourinho's comments evoked memories of his first spell in charge at Stamford Bridge between 2004 and 2007 when he regularly took Joe Cole to task in an attempt to achieve a high level of consistency from the skilful England midfielder.