Clarke reckons that Albion's next generation of players can learn a lot from the centre-half and his attitude towards his career.
"Jonas is one of the key players in our group and that's why we spent so long chasing him and making sure that he got a contract that would make him commit his future to West Bromwich Albion," said Clarke.
"He was a big 'signing' for us. Getting him and James Morrison to extend their contracts was important business.
"Jonas signing was one of the best. I wouldn't want to isolate anyone down to 'best' because the club have done a number of good things this season.
"It is a fantastic thing for young players to look at.
"Every young player who came out of the youth team, I told them not to worry about their next contract but the one after that.
"That tells you why Jonas is a top professional. He is a lovely fella. There are a lot of players like that. They are the devil on the pitch, angels off it."