England international Lallana left the South Coast for Liverpool for a reported £25m during the summer, with manager Ronald Koeman having recruited Tadic from FC Twente as a replacement for £15m less.
However, despite the difference in fees, Watson has insisted that he would "take" Serbian winger Tadic "over Lallana".
"I would take [Tadic] over Lallana. Adam had an outstanding season for us last year, but he could have been dropped after the first few games," Watson told the Daily Echo.
"Last season everything we did went through Adam. Not everything we do goes through Tadic. Tadic is just another part of a strong jigsaw."
Tadic has made eight appearances in all competitions this season, during which he has scored one goal.