Rodgers shelled out around £15m on the Spaniards during the summer, but neither has been able to force their way into the first team since their arrivals.
However, the Northern Irishman believes that the pair will justify their purchases when they become acclimatised to the Premier League.
"The likes of Aspas and Alberto have been at the club for a few months now and have seen the difficulties of playing in the Premier League, how hard it is and the physical demands," Rodgers told the club's official website.
"I can see them improving and working hard to fit into it. They will improve and get better in time.
"There was always going to be a period of adjustment."
The Reds host Norwich City this evening.