#1 Al Horford
Just like Gordon Hayward, Al Horford is a good player that the Celtics are overpaying. After spending his entire career with the Atlanta Hawks, the then 30-year-old joined the Celtics after signing a four-year, $113 million contract.
The 5-time All-Star is still one of the finest defensive players in the league, although he is averaging just 12.3 points this season while shooting .358 behind the arc. Horford has a player option on his contract worth $30 million for the 19/20 season, and this is a huge amount for the Celtics to invest on a 33-year-old.
With the Celtics being continually linked with a trade for Anthony Davis, moving Horford before the February trade deadline could boost the team's prospects of signing the Pelicans superstar this summer. Ultimately, Horford has performed well in Boston, although his contract will affect the team's ability to compete in the trade market.