"In a season with radical changes, we based our investment strategy on a three-year plan but after reaching the halfway point of this season, we have so far fallen short of the objectives," Godinho Lopes wrote in the club's newsletter.
The 2-1 loss at Braga left Sporting trailing leaders Benfica by 11 points, Porto by nine and they are three behind last year's Europa League runners-up Braga.
"We are aware of the points difference... it is out there for everyone to see. Sporting have to do more and to do it better to win," Sporting coach Domingos Paciencia told reporters.
In a twist of fate, it was unfancied Braga, Paciencia's previous club where he enjoyed so much success, who dealt the latest blow to Sporting's title aspirations.
"No-one can be happy, and the players even less. This was not the game we wanted," Paciencia said.
Sporting have not won the title since 2002, finishing around 30 points behind the champions in the last two seasons.
Although Paciencia remains popular with the fans the coach who arrived at Sporting in the close season and made wholesale changes to an ageing squad is under growing pressure.
"I am confident that, match after match, we will arrive to the level we aimed for and place Sporting where it deserves," Lopes said.
Sporting have at least reached the domestic cup semi-finals, unlike Porto and Benfica, and will play Legia Warsaw in the Europa League round of 32 next month.
