The Premier League's bottom club emerged from their trip to St James' Park with a point after a 1-1 draw, but were aggrieved not to have left with all three having seen Diame block Mike van der Hoorn's goal-bound effort with his arm before the break.
Carvalhal said: "After the game, I don't know if we have achieved one point or lost two, really, especially when I arrive in the dressing room and my players are really upset because there was the feeling that we could win this game".
"If a player comes off the bench and has an impact, and then continues pushing and working as hard as he was working, that's a very good message for the rest of the team".
He said: "We can not sell players that are playing because we would have to replace them for better players and, in January, we would need a lot of money to convince players to come here".
Benitez said: "I have heard people talking about our players but we do not have any offers. Without doubt Newcastle need to sign a striker, they are desperate for a striker, they do need to score some goals".
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He said: "It is a team that has a new manager and is doing well". But maybe we would have to pay £25million or something like that.
The striker was replaced by Joselu after Ayew handed Swansea the lead, and Benitez's switch paid dividends when the substitute levelled four minutes after coming on.
Newcastle pressed for a victor without creating many chances to find to it, and Swansea would have stolen the points had Wilfried Bony not seen a goal-bound effort cleared with Darlow stranded, the draw making it just one defeat in four in all competitions for Carvalhal, a run that will provide little solace for the Portuguese given the team's predicament.
Joselu's fourth league goal of the season sees him become their joint-top scorer along with Ayoze Perez, and Benitez took nothing but positives from his goalscoring contribution on Saturday.More news: Heaps of New Games and Ports Revealed for Switch
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