Doncaster have made forward Dany N'Guessan their sixth summer signing.
Tottenham have confirmed that Romanian defender Vlad Chiriches has completed a move to Napoli.
The 27-year-old, who moved to the Rotterdam-based side from ADO Den Haag in 2012, will now remain at De Kuip until at least the summer of 2017.
"I feel a lot of appreciation from the club, which is an important reason for me to stay at Feyenoord longer," Immers told the club's official website, feyenoord.nl.
"I'm really really enjoying myself and I feel completely at my place at Feyenoord. For me that was one of the conditions to stay here longer.
"I'll go on holiday first but I'm already looking forward to the first practice and the qualifying rounds of the Champions League."