There has been speculation about Kenny Miller's future

The 27-year-old has signed a three-year contract with the Premier League club but did not complete his move in time to play against Liverpool on Saturday.

"He is a proven goalscorer both at club and international level and gives us a different option up front," said Derby manager Billy Davies.

"He is a player with a never-say-die attitude and outstanding commitment."

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It had been reported that Miller was keen to leave Celtic to find regular first-team football.

Celtic signed strike duo Scott McDonald and Chris Killen during the summer and boss Gordon Strachan said this week: "I like good players around me.

"But the club has accepted a fee and Kenny might think that it's better to get a regular first-team place somewhere.

"He has been fantastic for us. Even when he was not at his best, he was a great team-mate, good in the dressing-room and he showed earlier in the season what a good player he is."

Miller hit three goals in his two appearances for the Hoops this season, but a hamstring injury ruled him out of Saturday's 5-0 win over Hearts and Wednesday's Champions League qualifier with Spartak Moscow.

The striker has previous experience of playing in England having spent five years with Wolves.