Sousa was sacked as manager of Queens Park Rangers on Friday after 'divulging highly confidential and sensitive information'.
The Portuguese tactician stated after the goalless draw with Crystal Palace that Blackstock, QPR's leading scorer this season, had moved to the City Ground without his knowledge.
Sousa said that he had given his players two days off after the recent defeat to Bristol City and that when he came back, he had been told by sporting director Gianni Paladini that Blackstock had linked up with Forest until the end of the season.
However, agent Eric Walters has now attempted to clarify the situation, insisting that there had been communication with both Paladini and Sousa.
"Dexter was unhappy at QPR for some time, as he had only started six of a possible 21 fixtures," Walters said in a statement released on the club's official website.
"He wasn't even on the bench for QPR's home fixture against Bristol City and seeing as he was the club's top goalscorer, Dexter was unhappy about this situation.
"A few clubs approached me for Dexter, including Nottingham Forest. I spoke with Gianni Paladini and he advised me that we needed to clear this with Paulo Sousa.
"Paulo came back from Portugal on March 26 at lunchtime. Dexter discussed the situation with Paulo, and he didn't say anything to Dexter about the possibility of him staying with QPR.
"At 4pm on March 26, Dexter signed the paperwork to complete his loan transfer to Nottingham Forest."