According to Voetbal International's Tim van Duijn, Brobbey has been left out of the squad as the striker isn't fully focused at the moment.
The 23-year-old striker is set for a transfer to Ligue 1 side Stade Rennes, with whom Ajax are negotiating and close to an agreement, but Brobbey does not know if he wants to move to the French club yet.
The youth academy product has not played a minute in an official match this season, having suffered an injury in the final preseason match against AS Monaco. Brobbey scored just four goals in the Eredivisie last season as the striker struggled with his form.
Cesc Fabregas's Como were interested in Brobbey earlier this summer, but the Ajax forward had no interest in joining the Serie A outfit.
Kenneth Taylor on his way out
Besides Brian Brobbey, midfielder Kenneth Taylor is also reportedly close to a move away from the Johan Cruyff ArenA. Taylor handed in a transfer request to manager John Heitinga earlier this week.
FC Porto are being named as a potential destination for the Dutch international, who has played 168 games for Ajax across all competitions. In case of Rodrigo Mora's departure, Porto and former Ajax manager Francesco Farioli will turn to Taylor as their top priority.
Ajax are expecting Brobbey and Taylor to leave and have been looking for replacements for both, but have not taken action as of yet due to a lack of funds.
The transfer window in the Netherlands closes at 23:59 CET on Tuesday, September 2nd.