Fulham head coach Slavisa Jokanovic admitted his side didn't offer enough quality in their 4-0 defeat to Bristol City and still need to gel.
Chelsea loanee Tammy Abraham scored his 10th goal of the season against the run of play with the Whites dominating the first half as they did in their EFL Cup tie on Wednesday.
However, the Robins took control after the break and Luke Freeman made it 2-0 after an amazing run from Lee Tomlin.
Bobby Reid made it three after robbing Jozabed on the edge of the penalty area and driving the ball past David Button.
McDonald was then sent off with 10 minutes to go for a challenge on Callum O'Dowda the match before Aden Flint fired home from a yard to complete the rout.
And Jokanovic bemoaned his side's lack of cutting edge as Fulham suffered a second successive loss to the Robins in a week.
“We didn't offer enough quality, character and we didn't deserve a different result. At the end of the day, it's completely realistic what we find today in our stadium,” he said.
“We were a little bit confused. We're not solid like we were. Before they scored the first goal we had two chances.
“We moved the ball well and shot 15 times but only had two on target.
“In the last four games, we scored one goal against Burton and we didn't find the end product. We are playing it around but in our box, we are not solid enough and in the opposite box we don't have the end product and, for all of us, we have to take one step back as we started in a different way.
“We were more compact, solid and aggressive. With new players we tried to dominate from the beginning.
“We've not found the best solution, especially after the international break. It's absurd this situation and making another improvement.
“We have to be clear what the best option is for us. I need to give the new players more time to understand what we want to do from pre-season.
“They arrived and they have their own style and we haven't adapted with the new faces.”
Fulham are set to appeal Kevin McDonald's red card although Jokanovic would like to see the incident again where the midfielder went in late on Callum O'Dowda.
He explained: “It's not an important moment. The referee was close to the situation and makes the decision.
“We're going to appeal. It's normal but I can't give you a thorough answer as I didn't see it very well.”
He was given hope by opposite number Lee Johnson, who felt the red card was harsh but he believed Scott Parker should have been dismissed in the first half.
The Robins boss said: “I didn't think it was a red. It was difficult to see. I'm only four inches from ground level in the dugout.
“I thought there was one before that and I was disappointed Parker wasn't sent off from a tackle from behind.
“In fairness to the referee, he was consistent with Jamie Paterson. Whether it was right or wrong, I'll let you decide.
“I was disappointed at half-time as I thought he should have gone and Slavisa did as well because he withdrew him at half-time.”