The Boston Celtics and Washington Wizards have emerged as the frontrunners to sign free-agent big man Al Horford, and a final decision is expected Saturday night, league sources told The Vertical.

Horford could sign a four-year, $113 million maximum contract to leave the Atlanta Hawks.

Horford, 30, pared down the teams on Saturday morning, league sources said.

Horford met with four teams Friday in Atlanta, including the Celtics and Wizards, sources said.

Horford, a four-time All-Star, could only return to the Hawks if he decided to take the team’s most recent offer and the franchise made a series of moves to clear the necessary salary-cap space – an option that has become increasingly remote, league sources said.

Horford had been negotiating a five-year contract with Atlanta, but talks stalled – and the Hawks moved quickly to sign free agent Dwight Howard and re-sign guard Kent Bazemore.

The Hawks risk losing Horford – as well as forward Paul Millsap, who is a free agent in 2017 – for nothing. Millsap has been involved in trade talks in recent days, league sources told The Vertical.

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