Qatar is "running out of time" to honour promised labour reforms before the 2022 World Cup, says Amnesty International.
Research by the human rights group found that the authorities in the Gulf state are "falling significantly short" in their efforts to protect the rights of two million migrant workers.
Amnesty said "important steps" to improve workers' rights had been passed since an agreement was signed with the United Nations' International Labour Organisation (ILO) in 2017.
But in a 19-page report titled 'Reality Check', the watchdog warned that "much more needs to be done" and that workers were still being subject to "exploitation and abuse".
In a statement, world football governing body Fifa said it "welcomes the important steps taken in recent months by the government of Qatar towards reforming its laws on the protection of workers' rights".
However, it added: "We share the view of Amnesty International that additional progress is needed for the full implementation of the commitments for comprehensive labour reform by the government of Qatar."
The Qatari government has not responded to a request for comment.
In 2010, Qatar controversially beat rival bids from the United States, Australia, South Korea and Japan to host the tournament, with hundreds of thousands of construction workers arriving from overseas.
The country is building seven new stadia to stage the tournament which has been moved to winter to avoid the country's extreme summer heat.
Amnesty acknowledges that Qatar has "finally begun a high-profile reform process" amid international pressure over worker deaths because of poor conditions.
They include new laws for a temporary minimum wage and a workers' insurance fund. The ILO has also set up an office in Doha to cooperate on labour-related issues.
The study is largely focused on government infrastructure projects, rather than World Cup construction sites, but it says that workers continue to be vulnerable to serious abuses, "sometimes amounting to forced labour and human trafficking".
It also said that despite promises of reform, and some improvements, there has been "no meaningful reform of the 'kafala' sponsorship system", which ties workers to their employer. Qatar promised to abolish kafala, described by human rights groups as modern-day slavery, in 2016.
Amnesty said that in addition to country-wide reforms, around 30,000 workers on projects specifically for the World Cup were supposed to have benefitted from stricter labour standards, ethical recruitment, timely payment, the banning of forced labour and new accommodation.
It concluded that while these had led to "some real improvements", they were "not universally respected", and that last year World Cup organisers admitted that contractors working on one of the stadiums had breached a summer working hours ban.
An audit of 19 contractors working on World Cup sites also found that abuses such as excessive working hours remained at a majority of the companies.
Amnesty director Stephen Cockburn said: "Time is running out if the Qatari authorities want to deliver a legacy we can all cheer… a labour system that ends the abuse and misery inflicted upon so many migrant workers.
"The authorities have been taking some important steps to protect labour rights but much more needs to be done. Holes in the reforms mean many workers are still stuck in harsh conditions."
The Amnesty report came as Fifa hailed an important milestone in preparations for the 2022 World Cup, with the creation of a joint venture with Qatari organisers responsible for the delivery of the tournament in less than four years' time.
Qatar has also been celebrating its national team winning the Asian Cup for the first time.
Amnesty calls on Fifa to "proactively seek to influence the Qatari authorities to fully and quickly deliver on their promised reforms so that the protection of all migrant workers may be a positive legacy of the World Cup".
The Fifa statement added: "Fifa continues to engage with the supreme committee for delivery and legacy and other parties towards ensuring respect for the rights of workers who are involved in Fifa World Cup-related activities.
"As part of these and other human rights-related efforts, we are in regular contact with Amnesty International."
Last month Hassan Al-Thawadi - head of the Qatar 2022 organising committee - told the BBC that there was "room for improvement" on worker pay, but said there was plans for a minimum wage and that progress on reforms would continue.