The French talisman has thrived in his first month in the Premier League, scoring three goals in his opening four games for the club since arriving from Eintracht Frankfurt.
Diop singled out the forward as a player who can do it all, from setting up chances with his physical play to finishing chances off himself, making it even harder to play against.
“Good players are horrible to mark,” he told the club’s official website.
“Seb [Haller] in particular is very strong, tall, and clever. He can play it simply but he can also score and he can pass well. You don’t know as a defender what he’s going to do next, so it’s very difficult to defend against him.”
Monday’s 0-0 draw against Aston Villa was the first game the 25-year-old has failed to score in, after a brace against Watford was followed by a simple finish in the 2-0 victory over Norwich City before the international break.
Haller has delivered a new dimension in the final third for the Hammers this season since arriving, with his physical presence something the likes of Marko Arnautovic just didn’t possess. The Frenchman has led the line for Manuel Pellegrini almost perfectly and attacking players such as Manuel Lanzini and Felipe Anderson have benefitted from that as well. The 25-year-old has won an average of 6.3 aerial battles per game according to WhoScored, which highlights how well he can keep possession for his side if the ball needs to be played long to release pressure on his teammates. Haller has also averaged 2.8 shots on goal so far in this campaign and looks a constant threat in-and-around the penalty area for his side. Diop is one of the strongest defenders in the Premier League, and for him to admit how horrible it is to mark his teammate only proves how much of a task defences have to keep him quiet in their games against the Hammers this season.