Northampton director of rugby Jim Mallinder was unhappy with referee Matthew Carley after late decisions cost his side dear in the 27-25 Aviva Premiership defeat to Saracens.
The Saints threw away a 12-point lead at Stadium MK as a weakened Saracens side fought back for victory.
Saints had overcome the injury losses of Louis Picamoles and Stephen Myler and seemed firmly in control having scored three tries through Harry Mallinder, Ken Pisi and Dylan Hartley.
Myler kicked two penalties and a conversion, with Mallinder also adding a conversion, but when Saracens built up some sustained pressure in the final stages a number of tight calls from referee Carley went again them.
Mallinder said: "I thought Chris Ashton knocked the ball in touch and we should have got a crucial line-out and then Ben Foden was taken out in the air.
"The TMO referred it back to the referee and, on that basis, he must have assumed something was wrong and everyone in the stadium could see it but surprisingly the referee stuck to his original decision when we should have had a penalty."
It was the third consecutive league game that Northampton had lost in the final moments, with Leicester triumphing 36-31 and Wasps 32-30, to seriously jeopardise their hopes of a place in next season's European Champions Cup.
Mallinder conceded: "It's really disappointing to lose but we needed a little bit of luck and more composure. We will need to keep looking at ourselves but it didn't help that we had our two key decision makers off the field.
"Louis has a bad neck while Stephen has a knee injury. Fingers crossed they will be okay for the Exeter trip as we now have a fortnight off.
"It will be tough down there so European qualification may come down to a winner-takes-all game against Harlequins in the final match of the season."
Saracens, without a number of leading players, struggled for any continuity and for most of the match the goal-kicking of Alex Lozowski seemed their only threat.
He kicked four penalties to keep his side in contention before the introduction of Billy Vunipola and Ashton galvanised the visitors, with Ashton and Marcelo Bosch scoring late tries which, coupled with a conversion and fifth penalty, got them over the winning line.
Saracens director of rugby Mark McCall said: "Our game wasn't up to the required level for the first 60 minutes as our set piece wasn't dominant.
"We had a decent bench and we got a bit cross after we conceded a soft third try and got up a head of steam in the final quarter as we carried a lot harder.
"It was a lesson for us as the big things have to be right and they'll need to be at Munster next Saturday if we are to win there.
"We knew we had to put them under pressure as they've lost a few games of late in the final minutes and Alex Lozowski helped by having a superb second half and should be picked for the England tour to Argentina."