Chelsea's attempts to sign Augsburg left-back Abdul Baba Rahman are being frustrated by their inability to offload Filipe Luis.
The 21-year-old has been earmarked to take Luis' place in the squad due to the latter's desire to return to Atletico Madrid.
However, Chelsea are demanding the £16m they paid Atletico for his services a year ago and the La Liga club, who are making attempts to sign him, have so far refused to do so.
Mourinho said: "If Atletico Madrid want him back then they have to pay and we have to discuss the offer.
"If he leaves then we have to react and we have to go in the market and find a replacement."
Chelsea potential arrivals and exits - July
Rahman has already received an offer to join Roma, but is believed to favour a move to the Premier League champions.
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