The 21-year-old attacking midfielder has made no secret of his desire to one day play in the Premier League, alerting the attention of a number of potential suitors.
"I think (a Spurs move) would be an error for him," revealed the French full-back. "I watch the French League and Hazard is an excellent player.
"It would be a major signing for Arsenal, but it's up to different people to decide his destination.
"He needs to reflect and make the choice of club for the style of football. If he goes to Spurs, he will be an enemy for me."
The last few weeks have seen Tottenham move to the forefront in the race to sign Hazard, but after Arsenal's impressive 5-2 victory over their local rivals in yesterday's north London derby, the fourth-placed Gunners have closed the gap in the Premier League to seven points.
"Hazard has the perfect profile for the Premier League," Sagna added. "He has swiftness, is a very good dribbler and is able to find spaces for teammates.
"He is a player who can change the rhythm and provoke problems in defence."