Delph has struggled with injuries over the course of his Villa career but he has established himself as a regular this season and scored the only goal in the win over Chelsea last time out.
Weimann feels the 24-year-old has been Villa's "best player all season" and backed Delph to continue improving.
He told the club's official website: "Fabian has been brilliant. It's as simple as that.
"He's been our best player all season. He's just been inspirational on the pitch and he's a top lad to have in the dressing room too.
"He's improving all the time. He's getting better and better with each passing week.
"He was so unlucky with injuries for quite a few years when he first arrived at the club.
"But this season he's not missed many training sessions at all. He's been on top form all season. There's been no dip.
"Fabian is the driving force for us in that midfield area. He's a leader in there."