Jurgen Klopp has conceded Liverpool miss Joe Allen after the Wales international swapped Merseyside for Stoke City during the close-season.
Allen headed for the bet365 Stadium after impressing at Euro 2016, having struggled to hold down a starting berth under both Brendan Rodgers and Klopp at Anfield.
And the 26-year-old has made a big impression since completing the switch, scoring five goals in 16 Premier League matches, with Stoke boss Mark Hughes expressing surprise this week that Liverpool allowed him to leave.
"Do we miss Joe Allen? Yes," Klopp said ahead of Tuesday's clash between the two clubs. "Unbelievable, strong player.
"We all knew his quality. He's having a big impact at Stoke.
"It was a common decision. It was clear after the last two years, not being a fixed line-up player.
"He plays a little more offensive now than what he would for us.
"If Liverpool sells a player, then they have to have a real impact at their next club. If you leave us, okay, then show us what you've learned."
Despite ongoing injury problems for key players such as Philippe Coutinho and Joel Matip (both ankle), as well as Sadio Mane's impending departure for the Africa Cup of Nations, Klopp insists he will not be hurried into any January deals.
"I think I have said one or two times, if there is something for us that makes sense and is possible, because there are other clubs, then it's what we always do," he said.
"I can say we don't want to convince players with money. We want to have players ready to develop.
"We have already very good players, and if somebody wants to be a part of this team then they're very welcome.
"I think usually in winter if you don't have the biggest injury issues in the world, and you need players for building a line-up then you should only do things you'd do in the summer.
"We always have an eye on the market but first of all I am really happy with this squad. We still have options.
"From the beginning of January Sadio will not be involved, but we still have options. We knew before with Sadio, it was part of the deal."