Jose Mourinho was disappointed by Manchester United's lack of first-half ambition in Thursday's 1-0 Europa League defeat at Feyenoord.
United, who made eight changes from the team that lost 2-1 to Manchester City in last Sunday's derby, were lacklustre in the opening 45 minutes at De Kuip in the Group A contest.
The Red Devils did show more urgency after the break, but were caught cold by Tonny Vilhena's 79th-minute winner despite suspicions of offside against Nicolai Jorgensen - who provided the assist.
And manager Mourinho accepts United were off the pace in the opening period.
"I think in the first half we did not have an especially ambitious attitude," he told a post-match news conference.
"I am not saying bad, but I'm saying not with the ambition you need to win football matches.
"The second half was different, it was exactly when we were trying to win and Feyenoord was trying not to lose that they scored the goal, which I think we didn't deserve."
Asked if that left him disappointed, Mourinho responded: "Yeah, I always expect maximum ambition and maximum focus it doesn't matter the competition or the opponent.
"I am very pragmatic in my approach to matches and competitions, the next match and next competition we play is always the most important.
"So I looked at this game, and you can say okay you changed eight players, but I played with a good team, I played with enough good players to win the match. In the second half they answered to my words at half-time."
Mourinho also rejected any notion that fatigue could be a problem in Sunday's Premier League encounter against Watford given the raft of changes he made to the starting line-up.
"First of all I have players that are not here, I have players that didn't play here for 90 minutes, so it's not a problem of accumulation," he added.
"We play midday Sunday, we are professionals, let's not make an excuse for Sunday because we have to play these games. They have to be fit, they are, and they have to be mentally strong."