The 28-year-old Portugal midfielder joined the English Champions until the end of the season.
Guus Hiddink has resigned as manager of Anzhi Makhachkala, the wealthy Russian club said in a statement on their website on Monday amid reports he was favourite to take over at Barcelona.
Ten-man Zenit St Petersburg beat Dynamo Moscow 2-1 on Saturday to claim a second consecutive Russian Premier League title with three games to spare.
News of all that's transpired on and off the football field
News of all that's transpired on and off the football field on Thursday
Zenit St Petersburg condemned violence by their fans during the 4-1 defeat by Austria Vienna in the Champions League on Wednesday, saying the trouble-makers led to the Russian team's poor performance.
Defending champions Bayern Munich must face Diego Simeone's Atletico Madrid after they were drawn together in Champions League Group A alongside Salzburg and Lokomotiv Moscow.
Fiorentina tore apart Italian rivals AS Roma to reach the Europa League quarter-finals with a 3-0 win that left their opponents' season in tatters and under-fire coach Rudi Garcia tottering on the brink of the sack.
Napoli's Marek Hamsik enjoyed a memorable return to his former club Slovan Bratislava, scoring one and creating another, in a 2-0 victory on Thursday as the Italians joined five others who made it two wins from two in the Europa League group stage.
Croatia defender Domagoj Vida apologised after his team's World Cup semi-final victory over England on Wednesday after speaking out in support of Russia's neighbour and adversary Ukraine.
Holders FC Barcelona have been placed in Group E, along with Bayer Leverkusen, AS Roma, Dinamo Zagreb.
Borussia Moenchengladbach's hopes of qualifying for the Champions League for the first time were hit by a 3-1 home defeat by Dynamo Kiev in the first leg of their playoff tie.
IMAGES from the Europa League matches played on Thursday
Relations between Ukraine and Russia remain highly charged following Moscow's 2014 annexation of Ukraine's Crimea region and its backing for a separatist rebellion in eastern Ukraine. Some Ukrainian politicians have called on countries to boycott the soccer World Cup, which Russia is hosting.
Holders Sevilla maintained their Europa League challenge with a 1-0 win over Rijeka in a winner-takes-all clash on Thursday.
Jonatan Soriano's love affair with the Europa League continued as last season's top scorer grabbed a hat-trick on Thursday to help Salzburg become one of four teams to reach the knockout stages.
Modest Braga, who have never won a Portuguese league title, stunned five-times European champions Liverpool 1-0 with a first-half penalty in the Europa League on Thursday.
Roman Pavlyuchenko is poised to join Tottenham Hotspur, the Russia striker said on Tuesday.
A summary of Tuesday night's matches in the Champions League.
Inter Milan defender Fabio Cannavaro has warned Champions League opponents Dynamo Kiev to banish thoughts of a classic Italian counter-attacking game.
The striker created the goals that secured Arsenal's place in the last 16 of the Champions League.
In other Champions League matches, Manchester United beat Scottish champions Rangers while Chelsea impressed while beating Lazio.
Inter Milan travel to Lokomotiv Moscow seeking to preserve their 100 per cent record in the Champions League this week.
Arsenal led a list of nine clubs who grabbed a second win in as many games in the Europa League group phase as France striker Olivier Giroud scored his 100th goal for the club in a 4-2 win at BATE Borisov on Thursday.
Croatia's Football Federation (HNS) sacked Ognjen Vukojevic, a member of the national team's coaching staff, over a "glory to Ukraine" video posted after Croatia beat Russia in the World Cup quarter-finals, HNS said in a statement on Monday.
Images from the UEFA Champions League matches played on Tuesday night.
Visitors Ajax had looked comfortable after former Southampton winger Tadic set up the first goal with a swerving cross before drilling home the second himself.
This week's digest of stories that are weird, true and funny.
The Champions League group stages took on a less predictable look after Thursday's draw, helped by UEFA's decision to tweak the seeding system.
Borussia Dortmund snatched a late goal at Atalanta to progress with a 1-1 draw, while AC Milan and Atletico Madrid, both with three-goal leads from the away legs, completed the formality of qualifying with 1-0 wins at home on Thursday.
Arsenal teenager Bukayo Saka scored his first goal for the club as they beat 10-man Eintracht Frankfurt 3-0, while Manchester United's 17-year-old Mason Greenwood secured a 1-0 win over FC Astana as the Europa League group stage began on Thursday.
Pep Guardiola will return to the Nou Camp in the Champions League group stage after his new club Manchester City were drawn against his former Barcelona team on Thursday. The two sides were drawn in Group C alongside Borussia Moenchengladbach and former European champions Celtic in one of the toughest of the eight sections. Spanish coach Guardiola, who won the Champions League twice with Barca, faced the Catalans when he was in charge of Bayern Munich two seasons ago and suffered a 5-3 defeat in the semi-finals.
Arsenal's young guns continued to shine as they dismantled Standard Liege 4-0 on a hectic night of Europa League action that produced a full house of Spanish victories on Thursday. A summary of the matches.
A round-up of Euro 2016 warm-up matches played on Sunday
Troubled AC Milan were held to a goalless draw by AEK Athens
The last-16 knock-out round kicks-off this week with Chelsea visiting Paris on Tuesday; Zidane to coach Real Madrid as manager in his first match in Europe
Kazakhstan's Astana fought back to beat a youthful Manchester United side 2-1 at home, Arsenal's woes continued as Frankfurt's Daichi Kamada scored twice to secure a 2-1 win.
Images from the Europa League matches played on Thursday
Two hundred years after George Stephenson built the steam-powered Blucher, Open Knowledge pays tribute to 200 years of rail transport.