The Blues have had two bids rejected by United for the England international but Mourinho has stated the club will strive until the end of the transfer window to add a striker to their squad.
As well as Rooney, Chelsea have been linked with a move for Samuel Eto'o, who could become part of a fire sale at Russian giants Anzhi Makhachkala, and Mourinho has confirmed the club have alternative attacking targets should a move for Rooney not come to fruition.
"We have plan B and C," Mourinho said. "Don't ask me names because it is difficult to speak about players from other clubs."
"When you think that you'd like to have one player and the market is open and the official bids are not forbidden - official bids are always accepted in an ethical way - you try because nobody forbids you to try.
"Of course, the players' owners can do exactly what we did with David Luiz and Barcelona. It's simple."
United are understood to have informed Chelsea that Rooney is not for sale at any price but that has seemingly not deterred the interest of Mourinho, who wants to add to his artillery despite having Romelu Lukaku, Demba Ba and Fernando Torres in his ranks.
Manager David Moyes has continually stated that Rooney is not for sale but the 27 year old's demeanour during his cameo appearance in the 4-1 win over Swansea City suggested he is far from happy with his current plight at Old Trafford.
Chelsea have already signing Marco van Ginkel and Andre Schurrle, both of whom featured in the opening weekend win over Hull City, as well as Marc Schwarzer but want further additions to boost their assault on the Premier League title.
The summer window closes 2 September, over two weeks after the start of the new season meaning plans ahead of games can often be disrupted by a club's transfer dealings. After receiving a bid for Yohan Cabaye from Arsenal on the eve of the league game against Manchester City, manager Alan Pardew was forced to leave out the Frenchman before criticising the length of the window.
And Mourinho concurs with the Toon boss: "At a certain point I agree with what Alan was saying, that the transfer window goes too far, the transfer window goes to the third, fourth fixture of the season, which I also agree that is too much," Mourinho said.
"But at the same time it gives everybody a chance to be in the market while we are winning or losing points.
"We have conditions to try to improve our team by bringing in one more player and we are going to try that till the end."
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