The Blues have allowed Romelu Lukaku to re-join Inter Milan on loan after a disappointing first season back at Stamford Bridge.
Chelsea had spent £97.5million to sign him from the Serie A club and he scored just 14 goals in all competitions, though that was still enough to be the club's top scoring player.
Tuchel has added Raheem Sterling in a £50m deal from Man City, who predominantly plays as a winger but has played through the middle for Pep Guardiola.
The club have been linked to Manchester United superstar Cristiano Ronaldo, with his agent reportedly holding talks with new Blues owner Todd Boehly.
A move for Bayern Munich superstar Robert Lewandowski has also been mooted.
The Chelsea boss is instead focused on bolstering his defensive line following the departures of Andreas Christensen and Antonio Rudiger on free transfers.
They are close to signing Kalidou Koulibaly from Napoli and will then target Presnel Kimpembe from Paris Saint-Germain and Nathan Ake from Man City.
Tuchel was asked about his plans to sign a new striker, but refused to comment on links to Ronaldo and Lewandowski.
"I would not rule it out [signing another striker] but right now it is not the priority. The priority right now is defence, it's not a secret. From there we need to see what's possible," he told Sky Sports.
"We're competing against the two top teams but Tottenham did a very active and aggressive and early transfer period, they have maybe the strongest squad they ever had with one of the best coaches in the world, Man Utd are never shy of recruiting with a new coach and Arsenal had some big signings already so we need to keep the level up to be competitive."