The pair played together at the Mestalla between 2010 and 2011, before Mata made the switch to Stamford Bridge, having also featured alongside one another for Spain.
Soldado followed Mata to the Premier League in August, and has scored twice for his new club from the penalty spot so far this campaign.
Mata has watched on with interest at his compatriot's start to life at Tottenham, and while he believes the 28-year-old can continue to improve, he refused to be drawn on whether he can rival the likes of Luis Suarez and Robin van Persie.
When asked if Soldado could compete with that duo for goals in the Premier League, Mata said: "Let's see.
"I really enjoyed it when I played with him for Valencia and with the national team," he added on Sky Sports.
"I think that he is doing really well. Last season, he scored a lot of goals, and this season, he has started very well. He's very good."
Mata has made just one Premier League appearance under new Chelsea boss Jose Mourinho this season, with reports in Spain on Friday linking him with a move to Barcelona.
