England goalkeeper Fraser Forster does not know if he will still be at Celtic when they next play in Europe.
Norwich captain Sebastien Bassong has signed a new two-and-a-half-year contract.
Ross County have signed Dutch winger Darren Maatsen.
The 22-year-old arrives from Dutch second-tier side Excelsior and is set to be among a number of players from Holland arriving in Dingwall.
County will also confirm a deal with 25-year-old midfielder Melvin de Leeuw when his contract with Cambuur expires.
Manager Derek Adams told the club's official website: "I am delighted to have signed Darren. He is a quick and skilful player who will suit our style of play next season."
Adams is looking to rebuild his squad after midfielders Iain Vigurs and Paul Lawson joined Motherwell, while Andre Hainault, Evangelos Oikonomou, Mark Fotheringham and Steffen Wohlfarth are not expected back next season.
County are also involved in a dispute with St Johnstone over the future of Richard Brittain after registering him with the Scottish Football Association for next season despite the midfielder having signed a pre-contract deal at McDiarmid Park.