Cardiff City manager Neil Warnock is unhappy with the way in which top scorer Kenneth Zohore's new contract was handled.
The 23-year-old had been at Cardiff City Stadium hours earlier than team-mates in order to put pen to paper.
"He's been at the ground since half past four so no wonder he's knackered," said Warnock.
The Bluebirds boss added: "I'm disappointed about that.
"He shouldn't have been in until half six, and the game should have come first really.
"It was something I wasn't aware of and it won't happen again."
The loss against promoted Newcastle was Cardiff's final home game of the season, with the Bluebirds' campaign coming to an end away at Huddersfield next weekend.
There has been speculation the game against the Magpies could also have been Peter Whittingham's final match at the Cardiff City Stadium.
Cardiff's longest serving player is out of contract at the end of the season and was given a warm ovation from the home fans as he was substituted during the second half against Newcastle.
As one of the club's top earners, Whittingham would have to take a pay cut if he signs a new deal, and Warnock has said the club will resume negotiations at the end of the season.
"We're talking all the time. I'm seeing Peter next week and I'm hoping to see a few of the other lads," Warnock added.
"We've managed to get Zohore over the line and now we're working on certain other players we feel can contribute for next season.
"We need quality in the forward line and find more goals, apart from that, it looks like an exciting time.
"I don't think there is a Brighton or Newcastle in the league next season so it will be very even.
"Even though we're not spending a lot of money, I think with what we've got and four or five additions, we can be up there.
"The bookies will have us just below halfway but you never know, if you get a team spirit like Brighton.
"It took them three years but we haven't got three years - at least I haven't - so we've got to conjure four or five new signings and give it a go."