The pair have both contributed to United's remarkable transformation this season and the former Melbourne Victory man relished his short time at the club.

"It's always going to be hard leaving, but especially because we're top of the league and going so well, and I was just starting to feel a part of that now, and to walk away from it is quite a strange feeling," Keenan told United's official website.

"I've loved being here. It helps that we've been winning whilst I've been here, but as a group of players, the coaching staff, the fans and supporters, it has been great and I've really enjoyed my time."

Keenan was signed as a short-term injury replacement for Nigel Boogaard.

Watson featured in all ten of United's A-League games since arriving at the club in July.