Mourinho has repeatedly said that he will not be overhauling his squad this month and that any business could be dependent on players leaving.
One player who appears to be on his way out of the club is midfielder Christian Eriksen, whose contact expires in June, but it is not certain he will depart this month.
Mourinho, whose side have stumbled in recent weeks, walked into the club with his eyes wide open and said he was on the same page as chairman Daniel Levy.
"That was very clear for me and is very important for me to understand that before I came," said the Portuguese boss, who took over from the sacked Mauricio Pochettino in November.
"This is our first transfer window, not the last," he added. "We are going to have one in the summer, we are going to have one in 2021 January, we are going to have another one in the summer of 2021.
"We are going to have to try to be intelligent and we have to try to make the right decisions, not just for now, but for the development of a cycle."
Spurs are struggling for numbers ahead of Sunday's FA Cup trip to Middlesbrough.
Harry Kane, Tanguy Ndombele, Ben Davies, Danny Rose and Hugo Lloris are all injured and many players have played three games over the Christmas period.
Mourinho said he was likely to call on youth at the Riverside but emphasised that such a move did not mean the FA Cup was not important for the eight-time winners.
"Everybody's going to be involved," he said. "If you go to our squad and no Rose, no Davies, no Lloris, no Kane. I don't know if Eric Dier will be ready but he is still to come back.
"When you say no, no, no, no, no you have to say (Oliver) Skipp, (Japhet) Tanganga, (Troy) Parrott, the young boys in.