Manchester United will make a bid to sign Thomas Muller from Bayern Munich this summer, sources have told ESPN FC.

With Radamel Falcao struggling for fitness and Robin van Persie now in decline, manager Louis van Gaal has identified the forward positions as one of five key areas to improve this summer, and sees his former protege Muller as an ideal fit for his versatility and his scoring rate.

The United boss managed Bayern in 2009-10, and that season gave the 25-year-old his first run of regular starts. Muller had previously made only five appearances for the German side, and is known to look up to his former boss.

United feel they can play on that to work a move, especially given the apparent discord between Muller and current Bayern manager Pep Guardiola after the forward was taken off during the German champions' Champions League semifinal first-leg defeat to Barcelona.

Thomas Muller was reportedly not happy at being substituted again Barcelona this month. Lars Baron/Bongarts/Getty Images

Bayern would have to sanction any sale, but it is generally expected that Guardiola will try to use to summer transfer market to bring the team more in line with his philosophy, and that could mean some big moves.

United would likely need to offer upward of £30 million to tempt Bayern.

Should Muller arrive, it is possible Van Persie could leave, and Juventus have reheated their interest in the Dutch striker from 2012, when they initially challenged United for his signature.