Dec 13 (Reuters) - Manchester United ( MANU ) players need more time to perfect newly appointed manager Ruben Amorim's 3-4-3 system, striker Rasmus Hojlund said on Thursday after he came off the bench to score both goals in the club's 2-1 Europa League win at Viktoria Plzen.

The Denmark forward, who previously said Ruben's formation suited his playing style, has scored five goals in six Europa League appearances this season.

"We still need more time. It's still very early days," the 21-year-old told TNT Sports.

"It's about getting the routines together and I think it's getting under the skin now, but obviously it still needs a lot of practice and a lot of time.

"We don't have a lot of sessions so we have to train it during the matches. I know it sounds a bit odd, but it's how you learn the best."

Hojlund said United had struggled with the weather conditions in Plzen earlier in the game, before staging a second-half comeback that sent them back into the top-eight of the competition as they seek a direct qualification to the round of 16.

"It was a bit difficult. Very cold today, difficult circumstances, the pitch was a bit boggy. We had to deal with it and we solved it in the second half," Hojlund said.

United, 13th in the Premier League, visit defending champions Manchester City on Sunday.