London: Manchester United have signed 19-year-old French striker Anthony Martial from Monaco on a four-year contract with an option for a further year, the two clubs announced on Tuesday.
United did not disclose the transfer fee, but British media reports said it was £36 million ($55.1 million, 49 million euros) -- a world record for a teenager -- and reports in France said it could rise to 80 million euros.
"I am so excited to be joining Manchester United," Martial told the United website. "I have enjoyed my time at AS Monaco and I would like to thank them and the fans for everything they have done for me."
News of United`s move for Martial sent shock waves across European football, with the former Lyon youngster having played just 72 games and scored 15 goals in his fledgling career.
But despite United having struggled for goals in the season to date, manager Louis van Gaal suggested that the quick, sure-footed attacker would be given a gentle introduction to English football.
"Anthony is a naturally talented, young, multi-functional forward with great potential," Van Gaal said. "We have been watching him for a while now and he has developed immensely during his time at AS Monaco.
"I am delighted he has joined Manchester United as I believe this is the right club for him to continue his development as a young player.
"He has all the attributes to become a top football player; however we need to give him time to adjust to his new environment and the rhythm of the Premier League."
Martial, who will wear the number nine shirt at Old Trafford, joined Monaco from Lyon for around five million euros in 2013 and broke into the first team only last season, scoring 12 goals in 46 appearances.
He was handed his first France call-up for the forthcoming friendlies with Portugal and Serbia and was allowed to leave their Clairefontaine training base on Monday in order to sign his contract and undergo a medical.
"I have always wanted to play in the Premier League and to join the biggest club in the world is what every young footballer dreams of," added Martial, who has represented France at every youth level from under-16 to under-21.
"I am looking forward to meeting my new team-mates and working with Louis van Gaal, who has achieved so much in his career."Should the transfer fee exceed 75 million euros, Martial would surpass Zinedine Zidane as the most expensive French player of all time.
Martial can play on the flanks, but his preferred position is at centre-forward and his arrival could see Wayne Rooney retreat to a number 10 role, having started the season as United`s lone striker.
United remain light on numbers in attack, however, with Javier Hernandez leaving for Bayer Leverkusen on Monday and Adnan Januzaj joining Borussia Dortmund on loan.
Robin van Persie and Radamel Falcao both left the club earlier in the transfer window.
Martial follows Memphis Depay, Matteo Darmian, Bastian Schweinsteiger, Morgan Schneiderlin and Sergio Romero in joining United and takes Van Gaal`s spending since his appointment last year above £250 million.
Monaco vice-president Vadim Vasilyev told his club`s website: "We wished to keep him this season, but Manchester United made an incredible offer that neither Anthony, nor AS Monaco, could refuse.
"Though this move was not planned, it shows the quality of the work undertaken by the technical staff, but also that we were right to recruit him two years ago. We wish Anthony the best for the next chapter in his career."
As well as Martial, Monaco have also sold Yannick Ferreira Carrasco, Geoffrey Kondogbia, Layvin Kurzawa, Lucas Ocampos and Aymen Abdennour in this transfer window, raising funds of around 170 million euros.
Lyon president Jean-Michel Aulas has revealed that his club stand to make 10 million euros as part of a sell-on clause agreed when Martial joined Monaco.