Wayne Rooney will have an injection in his left foot to enable him to play for Manchester United in their Champions League quarter-final second leg against Bayern Munich on Wednesday. David Moyes, the United manager, said there was no risk that the injury – a chipped bone – would be made worse and that it will not jeopardise the rest of the forward's season.

If Rooney were to suffer a further problem it could threaten his participation at this summer's World Cup. Four years ago he picked up a metatarsal injury when playing against Bayern in the quarter-final first leg in Munich and was replaced after 55 minutes. Although he recovered to start the return match, the England forward played only three more times for United that season and endured a disappointing World Cup finals in South Africa.

Moyes will start with Rooney with the tie poised at 1-1. "We think it's OK because we wouldn't do anything wrong," the manager said. "We take advice from our doctors. Everybody knows the character Wayne is and the kind of player he is. He is determined to play and if he is determined we would be mad not to [play him]."

on Tuesay morning Rooney joined the squad for the first time since picking up the injury during the home draw against Bayern. "He is able to train and is massively keen to be involved," Moyes added. "He's not trained all week so we need to be wary of that. He is happy to take an injection, which shows you his feeling for the game and the club."

Earlier Pep Guardiola, the Bayern coach, said he was "100%" certain Rooney would start. "He is going to play, 100%," he said. "I bet you a big, big glass of beer. I believe he is going to play, and [Antonio] Valencia, too."

As Robin van Persie is still sidelined because of a knee injury, Rooney's willingness to play is a major boost for United, with Guardiola clear about the threat carried by the England international. "He is one of the best players I have ever seen in my career," he said.

For United, a positive result is crucial. They stand seventh in the Premier League and are highly unlikely to secure a Champions League place, so their only hope of appearing in the competition next season is by winning it.

Moyes said: "We have to go into this game as a cup final for us. We went to be in the Champions League final but first we have to win this final, which is a second leg tie against Munich. We need a very good performance from everybody. It's a game where you cannot carry any passengers. It's a game everyone is ready for."I think the Champions League is a competition all sides are trying to achieve by reaching it. And it's no different at United. It's a competition that we have been one of the most successful clubs in Europe in, and it's a competition we want to try to continue in. It's a difficult task to get it through our league position this year but we will try and do it any way we can."

For the Scot, attempting to knock out Bayern represents the biggest challenge of his managerial career. "It's the hardest task because of the level of opposition and the competition and the stage. Of course it's the hardest game. . There are a lot of top players from both sides," he said.

Guardiola admitted he could be viewed as a failure if Bayern, already the Bundesliga winners, do not retain the European Cup and win the German Cup to repeat last season's treble. "I know if we are not in the final this club cannot deal with that," he said. "It's very important for me, for the team. I knew that before I came here. I knew right from the start they won the treble in the last season and I have got to be in the situation so that I can also get this treble. If I don't do that, then, hey it's not so good. I have to accept this situation."