The Norwich City defender has not featured for the Championship side since Neil Adams took over in April, before the club were relegated from the Premier League.
Adams did not involve the former Tottenham defender in the club's pre-season plans and hopes the move can help Bassong rebuild his fitness.
"It's important for Seb to get some first team football and keep himself fit and involved," Adams told Norwich's official website.
"So this is a good short-term loan move for all parties involved."
With centre-back Gabriel Tamas ruled out due to an anterior cruciate ligament injury, the 28-year-old will provide much needed cover at the back for Watford's new boss.
Jokanovic replaced Billy McKinlay earlier this week after the Scot had been in charge for just eight days, winning one and drawing the other of his two games at the helm.
Bassong's loan deal will see him remain at Watford, third in the league table, through the busy Christmas period and into early January.
