DC United acquire Lewis O’Brien

“I think he’s going to be a big help,” Rooney said. “He’s a very energetic player, good on the ball. … We’re lucky we were able to get him because he’s a very good player.”

However, O’Brien, 24, may not be around for long. The loan expires in mid-July, then United will have to extend it, take him on a permanent transfer – his market value is $9.6m according to transfermarkt – or have him return to England to start training camp.

“Even though it’s on a short loan, I think it’s a player who can really help us in the time he’s been with us,” Rooney said. “Beyond that, you never know. … We’ll see where we go.”

O’Brien, who is expected to be in contention for a spot, has become the third player to come out of the Premier League since last summer, alongside striker Christian Benteke (Crystal Palace) and midfielder Mateusz Klich (Leeds). His availability likely coincides with the return of Taxi Fountas, United’s best player last year, who has not played this season due to a hamstring injury.

O’Brien is young and well regarded in England but a strange series of events this winter left him ineligible for the remainder of the Premier League season. Nottingham Forest were preparing to loan him out to Flight Two’s Blackburn Rovers when administrative problems thwarted the last-minute move.

Anticipating the loan, Forest didn’t include him in their 25-man squad so the club scrambled to scout him for a place to play for the next few months.

O’Brien appeared in 13 of Forest’s 19 Premier League games, starting six and scoring once. He also played in four cup games and started twice.

Andy Najar paused for two to three weeks

Right-back Andy Najar will be out for two to three weeks with thigh and calf injuries, Rooney said. He was injured in practice late last week and did not play in Saturday’s 1-1 draw with Orlando City at Audi Field.

Brazilian Ruan replaced Najar last week and is likely to start on Saturday against New York City FC at Yankee Stadium.

Najar, who turned 30 on Thursday, has a long history of leg injuries, which is one of the main reasons the club took over Ruan from Orlando last offseason.

“We were obviously aware of that with Andy and we’ve been watching him throughout preseason,” Rooney said. “There might be certain days when he does something a little bit different or maybe stays at home. His hamstring isn’t too bad. The week before he got kicked in the calf so it’s a mix of both.” . . .

Eventually, with the terms of the contract settled, United brought in former Vancouver Whitecaps coach Carl Robinson as an assistant. He has been with the team since preseason and has been on the touchline for the first three MLS games.