The former Porto midfielder has impressed since his arrival.
"He looks a very good player - the kind we need," Johnson told liverpoolfc.tv. "He gives different ideas and movement and opens up defences.
"He's settled really quickly but generally when a new boss and new players come in it means it's going to take time for everything to settle down.
"It would have been silly for us at the start of the season to say we were going to go the season unbeaten and win everything before us because that just isn't football."