Manchester: David Moyes stepped up his quest for summer signings by flying to Lisbon on Wednesday night to check on at least three top transfer targets — and scupper Manchester City.

Sportsmail understands the two players under closest review were highly-rated centre back Eliaquim Mangala and his Porto team-mate Jackson Martinez. In addition, Manchester United boss Moyes has been alerted to the form of Benfica’s on-loan left back Guilherme Siqueira and was keen to see him in action.

Knowing he will be armed with a massive budget at the end of the season, Moyes attended Porto’s Portugal Cup semi-final with Benfica at the Estadio da Luz in an attempt to narrow down a long list of candidates to bolster his side in all areas.

Mindful that Mangala, 23, is also being considered by Manchester City as Manuel Pellegrini looks to bring in a defensive partner for skipper Vincent Kompany, Moyes seized the opportunity to run the rule over the linchpin of Porto’s back four before deciding whether to follow up his interest with a bid.

He is reluctant to meet the defender’s £37.8 million buy-out clause but may see if there is room for manoeuvre.

Colombia marksman Martinez, 27, has established himself as one of the Portuguese league’s most prolific finishers, and has attracted the attention of Roma, Arsenal and Chelsea as well as United.

Moyes has long been linked with Real Madrid left back Fabio Coentrao and is closing in on Southampton’s Luke Shaw, as revealed by Sportsmail on Wednesday. But he is keeping an eye on the form of Siqueira, who is on loan at Benfica from Granada.

Meanwhile, Toni Kroos has not agreed a move to Old Trafford, according to the Bayern Munich midfielder’s agent.

Reports had suggested that Kroos, 24, had agreed a £260,000-per-week deal to move to Manchester, but his agent Volker Struth has denied any agreement is in place. “We have not have not received any official contract offer [from Manchester United],” Struth told German paper Bild. “There is also no need to submit an offer as Toni will be with Bayern Munich until June 2015.”

Bayern boss Pep Guardiola has made it clear he wants Kroos to stay.

— Daily Mail