Steve Clarke pointed to mental fatigue as a factor behind West Bromwich Albion's surprise 1-0 home defeat against Fulham.
Clarke was critical of his side's performance in the opening 45 minutes, although he believes they played well enough after half-time to have deserved at least a point.
"The first half was poor but we were much better in the second," he said. "For what we did then, we deserved at least a point.
"We have set really high standards here and we didn't reach those in the first half. There were no raised voices at half-time - we just asked the players to dig deep.
"It's difficult playing four games in 11 days, physically, and there's a mental tiredness as well. "We asked them to find a way back into it and,credit to them, we did. Then we switched off and let them steal a goal on the counter-attack.
"That makes it doubly difficult because you then have to lift yourselves and we just couldn't get the second equaliser which I thought the second-half performance merited."
Albion have now last back-to-back games again after emerging from a recent four-game win-less sequence by beating Norwich and QPR in successive matches.
They are back at Loftus Road on Saturday, this time in the FA Cup, and Clarke is looking for greater defensive discipline from his side.
"Both their goals were disappointing," he added. "They were both avoidable. We switched off and got caught cold."
The Scot believes the contribution of goalscorer Romelu Lukaku typified Albion's afternoon.
"He was poor in the first half but much more of a handful in the second," he said. "He got himself another goal."