The United States midfielder arrived at Ewood Park last week on a loan deal that will see him at the club until the end of the season from Schalke.
His new manager said: "He's not even fully fit. He has not played for a number of weeks but he's got everything. I tried to say to him at the end, 'just save your legs a little bit', but he finds that difficult, he wants to tackle and join in.
"His passing and the way he kept the ball for us as well was fantastic. He was a £10 million player before his last injury and, with his performance here and another couple of games under his belt, I think he'll be fantastic for us."The Rovers boss has also hopes that his own actions of signing a new long-term deal may encourage his players to do the same and sign new contracts.
Kean said: “Having a long term contract means I can sit down with guys like Michel Salgado, Ryan Nelson and Chris Samba that want to extend their contracts.
“They were all saying ‘how long are you going to be here?’ And it was only, ‘well I’m here until the summer, hopefully longer.’ But now it is so I’m really encouraged by that.”