The former Coronation Street star is taking part in ITV's celebrity athletics contest The Games which has been airing live episodes all week up to the final on Friday.
But Thomas, 37, was left red-faced in Thursday's episode when his lycra cycling shorts split after his exertion at the velodrome.
His heavily-pregnant fiancee Lucy Mecklenburgh, who made a surprise appearance to support him at the event despite being due to give birth to their daughter any day now, posted a funny photo on Instagram of his bottom showing through his split shorts.
She captioned it: "Here it is again," in reference to Thomas' bottom making an appearance earlier in the week, too.
During the diving event, Thomas had sported a tiny pair of yellow swimming trunks which came off as he dove into the pool, leaving viewers with a more revealing sight than they were expecting.
Mecklenburgh, who posted Thomas' shorts split to her Instagram stories, also posted that she was surprising him at the velodrome with her sister Lydia after not having seen him since Sunday.
Ahead of The Games starting, Thomas had told This Morning that Mecklenburgh was extremely close to her due date.
He said: "If this little girl comes this week, I am out of the show.
"Fingers crossed I get to the end of it and I can finish it and complete it and then move on to the next chapter of our lives."
Thursday's episode also featured footage of a bike crash during the women's training at the velodrome which saw Olivia Attwood and Phoenix Gulzar-Brown fall from their bikes after crashing into each other.
Attwood lay on the track afterwards, tearfully explaining that the fall had sparked pain from a previous shoulder injury.
The Games final airs on Friday at 9pm on ITV.
Watch: Olivia Attwood injures her shoulder again in bike crash