(CNN) -- Bayern Munich completed the $50m signing of Spanish midfielder Javi Martinez from Athletic Bilbao, on Wednesday.
Martinez, part of the victorious Spain squad at the 2010 World Cup and the 2012 European Championship, had a $50m release fee in his Bilbao contract, but was required to pay the amount himself, which created huge tax liabilities for the player and complications for the German club.
Bayern's chairman Karl-Heinz Rummennigge described the transfer as "very complicated" and accused Bilbao of "refusing to cooperate from the very first day" of negotiations.
"We've had tax and legal problems to solve over the last few days, but fortunately we've succeeded," he said.
"The player has made an indirect contribution by foregoing a large sum of his salary. Our management is convinced the player will do very well with us," he added.
Despite being only 23, Martinez has made 201 appearances for Athletic Bilbao and was a key member of the side that enjoyed a surprise run to the final of last season's Europa League. The Basque native can play in central midfield, or as a center-back.
"Bayern are one of the best teams in Europe, and the whole world," Martinez told the club's website.
"There are so many top players here, all of them fantastic footballers. That's hugely motivating for me. And naturally, I'm looking to win trophies,"
In the English Premier League, Tottenham Hotspur announced the signing of Belgian midfielder Mousa Dembele from London rivals Fulham.
"We are delighted to announce that we have reached agreement with Fulham for the transfer of Mousa Dembele," Tottenham announced on their website.
Neither side confirmed the fee involved, but it is believed to be in the region of $24m. Dembele was signed as a striker for Fulham from AZ Alkmaar ahead of the 2010-11 season, but thrived for the club after moving into a midfield role
"Dembele originally joined Fulham as a forward, although his ability to drive forward with the ball and his eye for a pass saw him played in an attacking midfield role last season, a move that proved a huge success," explained a statement on the club website.
Tottenham will be hoping the 25 year old can replace Luka Modric, after the creative Croatian midfielder completed his moved from Spurs to Real Madrid earlier in the week.
"Following two full seasons at Craven Cottage, the Club would like to thank Mousa for his contribution and wish him well throughout the rest of his career," Fulham said in a short statement on their website.
In Italy, AC Milan further strengthened their attacking options with the capture of Bojan Krkic on a year long loan from Serie A rivals Roma.
Krkic joined Roma from Barcelona last summer for $15m, but the Spanish club have the option to re-sign the player next summer for $16.25m.
After making more than 100 appearances for Barcelona, Krkic enjoyed a fruitful debut season in Italy, scoring seven goals in 33 appearances. AC Milan will be hoping the young forward can help replace Zlatan Ibrahimovic, who moved to Paris St-Germain earlier in the season.
In his final season at Barcelona, Krkic was, coincidentally, chosen to replace Ibrahimovic as Barcelona's number nine after the Swedish striker moved to AC Milan.
Also on Wednesday, Bayer Leverkusen completed the signing of former Bayern Munich goalkeeper Michael Rensing, who was released by Cologne following their relegation last season.
"We have signed an experienced and high quality back up for our number one," explained Leverkusen managing director Wolfgang Holzhauser on the club's website.
"We've made this move as we are involved in three competitions."
North German side Hamburg have also made moves to strengthen their side before the close of the transfer window. Czech midfielder Peter Jiracek has moved from Wolfsburg, signing a four year contract with the Rothausen.
In Spain, Atletico Madrid strengthened their defence with the capture of Domingo Cisma from Racing Santander. The defender played for Atleti's youth teams and declared he was "back to stay" at the club, despite only signing a one year deal.
"A special group of players is being assembled here and I hope my arrival will increase the competition for places," he said.
Real Betis have completed the signing of French born Poland international Damien Perquis from Sochaux. Perquis has signed a three year contract after impressing during his brief appearances at Euro 2012.