Luton have signed former Peterborough and Brighton striker Craig Mackail-Smith on a two-year deal.
Norwich City have completed the signing of goalkeeper Jake Kean following his release from Blackburn Rovers.
Chelsea have been monitoring the defender for the past three months with scouts watching the Cameroon international in action last weekend, whilst Arsenal and AC Milan are also said to be interested.
Nkolou has agreed with the French outfit that he can leave in the summer if they receive an offer they are happy with.
He said: "I need to finish the season in a strong position, I am not thinking about any transfer at the moment."
Nkolou, 22, stated in December that he could not guarantee that he will be staying at Marseille in 2013 but insists his priorities currently remain with the Ligue 1 side.
"I want to help Marseille to finish with a trophy this season, my future will be discussed at the end of the season, "he added.
Tottenham were also said to be in the hunt for the defender but have seemed to ease on their interests for the player.