Eriksen, whose Tottenham contract expires at the end of the season, has been well below his best for much of the campaign and was criticised by Spurs fans following his lacklustre display in Saturday's 1-0 defeat to Liverpool.
Reports have suggested Eriksen has agreed terms with Italian side Inter, but Mourinho seemed to rule out an imminent transfer when he said the 27-year-old will be involved in Tuesday's third round replay due to the number of injuries in his squad.
"He plays tomorrow. After that I have a match on Saturday and he maybe plays on Saturday again. I cannot tell you much more than that," Mourinho told reporters on Monday.
Eriksen, who has scored just two goals for Tottenham this season, was interpreted as saying farewell to the club when he handed his shirt to a fan and waved to the crowd after the Liverpool loss.
Even if no deal is done this week, he could still move before the transfer window shuts at the end of January or sign a pre-contract arrangement.
Asked if he had noticed a dip in Eriksen's form, Mourinho conceded the playmaker hasn't been able to tune out the background noise about transfers.
"If you ask me the reasons, I am not an idiot, I have been in football many years," he said.
"A player in this situation, even if he wants -- and I am not criticising him -- it's normal a player in this situation doesn't perform in the highest level.
"But he is helping us in matches he has played for us. He's had positive performances and contributions like against Olympiakos and Norwich."
Whether or not Eriksen leaves before the end of the month, Tottenham are set to sign Benfica midfielder Gedson Fernandes on an 18-month loan.
The 21-year-old, who was also a target for West Ham, is reported to be having a medical at Tottenham on Monday.
But Mourinho was in no mood to give anything away about the player who could become his first signing since replacing the sacked Mauricio Pochettino.
"I am waiting for news. But news can come or not. I am more worried about Middlesbrough than the market," Mourinho said.
"With the rules even if we get the player you cannot play him in a replay so in this moment I am not interested in Gedson or any other players who could come.
"I don't know if we are getting. I don't think the Benfica president and coach, both my friends, will be happy if I speak about one of their players."