Gonzalo Higuain has been left out of AC Milan's squad for their match against Genoa on Monday amid reports of an imminent move to Chelsea.
The Blues have been linked with a move for the 31-year-old Argentina international, who excelled under Maurizio Sarri at Napoli and is currently on loan at Milan from Juventus.
Speaking at a press conference ahead of the Genoa clash, Gattuso admitted speculation has disrupted preparations.
He said: "I want to be honest with you all. We had a poor training session today due to all these rumours. We spoke after the training session and I did not consider him ready for this game.
"I accept his decision. Surely he could have done more and maybe we could have helped him fit in better.
"Right now we have to work with professionalism and determination, all these rumours have not helped us lately and we have to look ahead."
Sarri launched an unexpected rant at his players in his post-match press
conference on Saturday following the 2-0 Premier League defeat at Arsenal.
Speaking in his native Italian, an angry Sarri accused his squad of being
"extremely difficult" to motivate.
Eden Hazard played in a false-nine role in attack with former Arsenal striker Olivier Giroud on the bench for the visitors and Spain international Alvaro Morata not included.
However, former Rangers midfielder Gattuso is only concerned with his own team.
He added: "I am more worried about how to transmit calmness to the players and how to field the best team.
"Tomorrow we will be without four players and I am a bit worried. We have to put it aside and play with enthusiasm."
