Middlesex managing director of cricket Angus Fraser has queried the resolve of some of his side's players.
The Lord's side only avoided relegation on the last day of the season.
"Everybody's careers have highs and lows but at times we play some careless, soft, sloppy cricket," Fraser told BBC London 94.9.
"There are questions being asked about a few players in our side - is there really a steely backbone to them and are they tough enough?"
|Middlesex managing director of cricket Angus Fraser:|
|"Our target every year is to build on what we have achieved previously and to improve on it. This year we haven't and we've gone backwards."|
Middlesex won four of their opening six County Championship games of the season but then failed to win any of their remaining 10 first-class matches of the campaign.
The north London club were sucked into the Division One relegation battle and only retained their top-flight status after securing draws at Somerset and Lancashire in the final two matches of the season.
"There is so much talent in the dressing room and so many gifted cricketers but the frustration is when we don't get it out of them," Fraser said.
"We made lots of mistakes throughout the year. We can play well for long periods of time but we spoil it with a bad session.
"Our target every year is to build on what we have achieved previously and to improve on it. This year we haven't and we've gone backwards.
"We need to make sure we start performing to the levels we know we're capable of and have shown in this division in previous years.
"We have got to sit down and analyse everything we are doing for next season to make sure that if we do get in a rut that somehow we can find a way out of it."
Meanwhile, Fraser says one of his immediate concerns is identifying a replacement for captain Chris Rogers next season.
The 37-year-old batsman, who scored 1,333 Championship runs at an average of 55.54 this season, is set to be away for much of 2015 because of international commitments with Australia.
Australia have a tour of West Indies next May and then come to England for an Ashes series, which will run until late August.
"I can't see Chris not being selected for Australia," Fraser said.
"We will undoubtedly see him back in a Middlesex shirt again in years to come.
"Filling the void that he potentially leaves is something that is going to take quite a player to do.
"We have got to try to do that and get more out of the players in the dressing room on a more consistent basis to fill that void."