Whatever problems Manchester United had on the pitch last night, the club’s visit to the Olympic Stadium in Rome will be remembered for the violence inflicted on their fans outside the ground and for the heavy-handed policing that led to more casualties inside it.

United lost the first leg of their Champions League quarter-final against AS Roma 2-1 and will be without Paul Scholes for the return leg after he was sent off in the first half, but for the second successive away tie, trouble involving their supporters overshadowed the match.

Eighteen United followers were injured in clashes with Roma’s fanatical “Ultras” outside the stadium, local agencies reported, and one was taken to hospital in a serious condition with a knife wound to the neck. However, some of the worst scenes took place inside the ground as the security forces appeared to overreact to the rival groups throwing missiles.

Police with batons and riot shields charged into the section containing United supporters in an echo of their treatment of England fans in the same area of the same stadium during a qualifying match for the 1998 World Cup. Uefa immediately announced that it will launch an investigation. William Gaillard, the communications director, who was in the stadium, said: “I only saw glimpses of what went on, I saw some missiles flying and the police charging. We will be waiting for the delegate’s report and the control and disciplinary body will be looking at the television images to see the dynamics of what actually happened.”

United’s away match in the previous round of the Champions League, against Lille at the Félix-Bollaert Stadium in Lens, was marred when riot police fired teargas at their supporters. “We will also have to see what role Manchester United fans had in the incidents because they had some problems in Lens earlier this year,” Gaillard said. Roma could face disciplinary action if they are judged to have failed in their security arrangements.

The Independent Manchester United Supporters’ Association is compiling a dossier to submit to Uefa and has asked supporters to submit statements and pictures of the incidents. “The club issued warnings to our fans making it clear that they thought that there was danger of attack from the Roma fans,” the group said last night. “The Italian police were stationed on our side of the fence, in attack formation against United fans, in a way that only made sense if they were trying to protect the Roma fans from us. There is something very wrong here and we aim to get to the bottom of it.”

A United fan in the ground described the scenes to BBC Radio 5 Live. “At the time of the sending-off there were missiles exchanged and after the \ Roma goal their fans charged the United section,” he said. “The police got involved with a baton charge and all hell broke loose. You had seats being thrown at the police. Most of the missiles being thrown are bottles which are being sold inside the ground.”

Sir Alex Ferguson, the United manager, would not discuss the trouble and had no complaints about Scholes’s first yellow card, but thought the second harsh and blamed Cristian Chivu, the Roma defender, for persuading the referee to show it. “Chivu got him sent off,” he said. Roma then took the lead through Taddei and though Wayne Rooney scored his first goal in the Champions League proper since his debut hat-trick against Fenerbahçe in September 2004, Mirko Vucinic won the tie for Roma.

Chelsea had Didier Drogba to thank for keeping their hopes alive. The striker became the first Chelsea player to score 30 goals in a season for more than 20 years, heading the second-half equaliser against Valencia at Stamford Bridge after David Silva’s spectacular opener for the Spanish team.