"I asked the players to make it difficult for me to leave them out of the starting team on Sunday and the majority have made it very easy for me," said caretaker manager David Unsworth.
"We just can't concede the way we have done in the last ten minutes, it is just unacceptable and really disappointing. I’d love to think every single player is hurting the way I am at the moment. If they aren’t, they shouldn’t be here."
Unsworth took interim charge of the team following the sacking of Dutch manager Ronald Koeman on October 23.
While the club have been linked with several possible replacements they have been unable to secure a new manager, leaving under-23 coach and former player Unsworth in charge of a team currently in 16th place in the Premier League.
Unsworth has made no secret of his desire to secure the job on a permanent basis but the mauling at the hands of the 12th best team in Serie A will have done little to enhance his chances.
"It's an honour for me to be manager ... but at the same time you need the players to come with you, you need the players to give everything they've got. We've had that up until tonight," added Unsworth.
"We're asking players to run harder, to work harder than they've been used to. Some can, and some can't."
The club, who spent 149 million pounds ($198.24 million) on new players in the close season, have most recently been linked with Watford's Portuguese manager Marco Silva.
Former England captain Wayne Rooney, who started Thursday's game, said the defeat was "upsetting".
"There was nothing riding on the game, but it's our pride. It's not nice to lose games. It's very disappointing and upsetting," he said.
Asked about the club's search for a new manager he said:
"That's down to the board, it's their decision. Since David Unsworth has come in there's been a great atmosphere among the players and some positive results. The board have a decision to make and I'm sure they're working on it."
(Reporting by Simon Evans)
