It has the second time Loftus-Cheek has temporarily left Stamford Bridge, having spent a successful campaign with Crystal Palace in 2015/16.
Like his time at Selhurst Park, Loftus-Cheek has shown he is more than capable of playing at the Premier League level.
A rangy attacking midfielder, the London native has started 12 of Fulham's last 13 league matches, and former Cottagers midfielder Clark thinks he has been pivotal to the club being just two points from safety.
At the international level, Loftus-Cheek has won 10 caps for England but is behind the pecking order in Gareth Southgate's midfield stocks.
And Clark says the Englishman should consider leaving Stamford Bridge if he is not guaranteed playing time in order to further his domestic and international career.
"He's got terrific attributes and is technically very gifted with great ability. He can see a pass, go past people, great vision, can deliver the pass short or long.
"And if he goes back to Chelsea and it's difficult for him to break through, then yes, I think he has a decision to make.
"He has got to decide for his own future, for his career, for his England career. He's already got caps but he can get a lot more if he's playing regularly. Ruben has got to play in the Premier League week in, week out, and be one of the first names on the team-sheet."
Clark added that he would like to see Loftus-Cheek add more goals to his game, with the attacker scoring just once in 21 league matches this season.
"His ability is good enough to make sure he does that, he just needs to add the little bits to the end of it because he's certainly got the ability to score double figures in terms of goals. I think that's the missing ingredient at the moment.
"The key for Loftus-Cheek is to add more goals to his game and speak to Chelsea and find out if he has got a position there as a regular. If not then he has to, in my opinion, find a club who can give him that."