The Ghana midfielder moves to city rivals AC Milan on loan from Inter, Vincenzo Iaquinta joins Cesena on loan from Juventus, and Vedran Corluka links up with Bayer Leverkusen until the end of the season.
European transfer window: Muntari swaps blue for red in Milan
The Ghana international midfielder, who becomes a free agent in the summer, has made just four league appearances for the Nerazzurri in Serie A this season.
A statement from AC Milan read: "AC Milan announces it has acquired Sulley Muntari on a temporary loan."
Milan opted to make a move for the 27 year old after losing midfielder Alexander Merkel last week to a knee injury for two months.
Merkel only returned to Milan earlier this month in joint ownership from Genoa with the Rossoneri facing a shortage in midfield because of injuries to Mathieu Flamini, Gennaro Gattuso and Alberto Aquilani.
Muntari became the Italian club's fifth reinforcement in the winter transfer window and their second of the day after teenage Austrian striker Philipp Prosenik joined from Chelsea on a permanent transfer for an undisclosed fee.
Milan said in a statement: "Philipp Prosenik's contract has been deposited with the Lega Serie A."
Prosenik, 18, joined Chelsea in the summer of 2009 from Rapid Vienna. The Austria Under 19 international is the son of former Austria international Christian Prosenik.
Also in Italy, Vincenzo Iaquinta, the Juventus striker, will play on loan at relegation-threatened Cesena until the end of the season, the Turin giants confirmed.
Iaquinta, who is under contract with Juve until June 2013, has not played since March due to injuries and lack of form.
A statement from Juventus read: "Vincenzo Iaquinta will continue his career in Cesena.
"Juventus has reached an agreement with the Romagnola club to loan the player until June 2012."
Iaquinta, 32, moved to Juve in the summer of 2007 from Udinese and has scored 40 goals in 108 appearances for the club.
A World Cup winner with Italy in 2006, Iaquinta is ready for a new challenge.
"I haven't played since March," he said. "I've chosen Cesena because it's the right place to relaunch my career."
Juve also confirmed the midfielder Michele Pazienza will play on loan at Udinese until June.
Pazienza joined Juve on a free transfer from Napoli last summer and has made nine appearances for the club so far.
In Spain, Espanyol confirmed the signing of Victor Sanchez, following the Spanish player's release by Swiss club Neuchatel Xamax.
The Barcelona-based side announced they had agreed a deal to sign the midfielder on a three-and-a-half-year contract, after his previous employers were expelled from the Swiss top flight over administrative and financial issues.
He becomes their third signing of the window, after Philippe Coutinho joined from Inter Milan and another former Neuchatel player - the Nigerian striker Kalu Uche.
A statement on Espanyol's official website read: "Victor Sanchez, who has signed for us until 30th of June of 2015, arrives with our team to contribute with his versatility in the midfield or in defensive tasks, as well as with his experience gained in the different teams he has played for."
In Germany, Bayer Leverkusen signed the Croatia defender Vedran Corluka from Tottenham Hotspur on loan until the end of the season.
Leverkusen also obtained an option to sign Corluka on a longer contract, without elaborating. At the same time, Michael Ballack's agent said the former Germany captain would not be leaving the club immediately.
Rudi Voeller, the sports director, said Corluka was exactly the kind of versatile defender Leverkusen was looking for. "He can play not only right-back, but also in central defence and on the left," he said.
Wolfgang Holzhaeuser, the Leverkusen chief executive, added: "With this signing, we've got a high-level option.
"Corluka is a respected professional who will give us an immediate impact in class."
In France, Lorient signed Wesley Lautoa from Sedan on a four-and-a-half-year deal.
The 24 year old, who was born in Epernay but represents New Caledonia at international level, can play in defence or midfield.
"I come here to try to play as often as possible and to move forward, putting myself at the service of the team," he told the French club's website.