Sporting president quits after home defeat
"For various circumstances, I believe that it is best for Sporting's future that I no longer be the president of this great club," Bettencourt said on Sporting's website.
Sporting have been inconsistent since coach Paulo Sergio took charge at the start of the season, performing well in the Europa League but were knocked out of the Portuguese Cup in the early rounds. They will fall 16 points behind Porto in the league if the leaders beat Naval on Sunday.
Bettencourt was elected president in June 2009 with a landslide victory of around 90 percent of the votes. One of his first moves was to retain Paulo Bento as coach, but the strategy did not work out and Bento resigned in November.
The president appointed Carlos Carvalhal as interim manager and then replaced him with Sergio, with fans critical of the decisions due to both coaches' lack of experience at big clubs.
Bettencourt was also criticised for unsuccessful forays into the transfer market, particularly the expensive acquisition of French striker Sinama Pongolle from Atletico Madrid, and for selling captain Joao Moutinho to Porto and then calling him "a rotten apple."