"It is never easy for a new player to come into a new team, especially if the team does not play well," said the Reds boss.
"I was pleased with the way Dossena and Keane worked against Standard Liege but I know that they will both play better.
"They are both players with quality and they are both internationals so I am sure that they will improve.
"Sometimes a player can come into a team and do well straight away but usually they need time to adjust.
"When we signed Skrtel some people were saying he was not good enough after just one game but we all know of his quality now."