Owen Coyle tried to sign Stuart Armstrong last year and says the Celtic midfielder's value has gone up "four, five, six times".
Scottish Premiership Football
Former Rangers captain Barry Ferguson believes the club's new signings will need to "get up to pace pretty quick".
Young defender Daniel Higgins and experienced midfielder Alan Power join Kilmarnock on two-year contracts.
Hearts are in talks with the former Rangers striker Kyle Lafferty about a move to Tynecastle.
Audio & Video
Celtic striker Leigh Griffiths responds to comments by Rangers chairman Dave King that Celtic should be further ahead of their rivals.